abstract vs introduction research paper

• Manuscript Preparation

Differentiating between the abstract and the introduction of a research paper

• 3 minute read
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Table of Contents

While writing a manuscript for the first time, you might find yourself confused about the differences between an abstract and the introduction. Both are adjacent sections of a research paper and share certain elements. However, they serve entirely different purposes. So, how does one ensure that these sections are written correctly?

Knowing the intended purpose of the abstract and the introduction is a good start!

What is an abstract?

An abstract is a very short summary of all the sections of your research paper—the introduction, objectives, materials and methods, results, and conclusion. It ends by emphasising the novelty or relevance of your study, or by posing questions for future research. The abstract should cover all important aspects of the study, so that the reader can quickly decide if the paper is of their interest or not.

In simple terms, just like a restaurant’s menu that provides an overview of all available dishes, an abstract gives the reader an idea of what the research paper has to offer. Most journals have a strict word limit for abstracts, which is usually 10% of the research paper.

What is the purpose of an abstract?

The abstract should ideally induce curiosity in the reader’s mind and contain strategic keywords. By generating curiosity and interest, an abstract can push readers to read the entire paper or buy it if it is behind a paywall. By using keywords strategically in the abstract, authors can improve the chances of their paper appearing in online searches.

What is an introduction?

The introduction is the first section in a research paper after the abstract, which describes in detail the background information that is necessary for the reader to understand the topic and aim of the study.

What is the purpose of an introduction?

The introduction points to specific gaps in knowledge and explains how the study addresses these gaps. It lists previous studies in a chronological order, complete with citations, to explain why the study was warranted.

A good introduction sets the context for your study and clearly distinguishes between the knowns and the unknowns in a research topic.

Often, the introduction mentions the materials and methods used in a study and outlines the hypotheses tested. Both the abstract and the introduction have this in common. So, what are the key differences between the two sections?

Key differences between an abstract and the introduction:

• The word limit for an abstract is usually 250 words or less. In contrast, the typical word limit for an introduction is 500 words or more.
• When writing the abstract, it is essential to use keywords to make the paper more visible to search engines. This is not a significant concern when writing the introduction.
• The abstract features a summary of the results and conclusions of your study, while the introduction does not. The abstract, unlike the introduction, may also suggest future directions for research.
• While a short review of previous research features in both the abstract and the introduction, it is more elaborate in the latter.
• All references to previous research in the introduction come with citations. The abstract does not mention specific studies, although it may briefly outline previous research.
• The abstract always comes before the introduction in a research paper.
• Every paper does not need an abstract. However, an introduction is an essential component of all research papers.

If you are still confused about how to write the abstract and the introduction of your research paper while accounting for the differences between them, head over to Elsevier Author Services . Our experts will be happy to guide you throughout your research journey, with useful advice on how to write high quality research papers and get them published in reputed journals!

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Abstract Vs. Introduction — Do you know the difference?

Ross wants to publish his research. Feeling positive about his research outcomes, he begins to draft his manuscript. After completing the abstract, he proceeds to write the introduction. That’s when he pauses in confusion. Do the abstract and introduction mean the same? How is the content for both the sections different?

This is a dilemma faced by several young researchers while drafting their first manuscript. An  abstract  is similar to a summary except that it is more concise and direct. Whereas, the  introduction  section of your paper is more detailed. It states why you conducted your study, what you wanted to accomplish, and what is your hypothesis.

This blog will allow us to learn more about the difference between the abstract and the introduction.

What Is an Abstract for a Research Paper?

An abstract provides the reader with a clear description of your research study and its results without the reader having to read the entire paper. The details of a study, such as precise methods and measurements, are not necessarily mentioned in the abstract. The abstract is an important tool for researchers who must sift through hundreds of papers from their field of study.

The abstract  holds more significance  in articles without open access. Reading the abstract would give an idea of the articles, which would otherwise require monetary payment for access. In most cases, reviewers will read the abstract to decide whether to continue to review the paper, which is important for you.

Your abstract should begin with a background or objective to clearly state why the research was done, its importance to the field of study, and any previous roadblocks encountered. It should include a very concise version of your methods, results, and conclusions but no references. It must be brief while still providing enough information so that the reader need not read the full article. Most journals ask that the abstract be no more than 200–250 words long.

Format of an Abstract

There are two general   formats — structured and unstructured. A  structured abstract   helps the reader find pertinent information  very quickly. It is divided into sections clearly defined by headings as follows:

• Background : Latest information on the topic; key phrases that pique interest (e.g., “…the role of this enzyme has never been clearly understood”).
• Objective : The research goals; what the study examined and why.
• Methods : Brief description of the study (e.g., retrospective study).
• Results : Findings and observations.
• Conclusions : Were these results expected? Whether more research is needed or not?

Authors get tempted to write too much  in an abstract but it is helpful to remember that there is usually a maximum word count. The main point is to relay the important aspects of the study without sharing too many details so that the readers do not have to go through the entire manuscript text for finding more information.

The  unstructured abstract  is often used in fields of study that do not fall under the category of science. This type of abstracts does not have different sections. It summarizes the manuscript’s objectives, methods, etc., in one paragraph.

Related: Create an impressive manuscript with a compelling abstract.   Check out these resources and improve your abstract writing process!

Lastly, you must check the author guidelines of the target journal. It will describe the format required and the maximum word count of your abstract.

What Is an Introduction?

Your introduction is the first section of your research paper . It is not a repetition of the abstract. It does not provide data about methods, results, or conclusions. However, it  provides more in-depth information  on the background of the subject matter. It also explains your hypothesis , what you attempted to discover, or issues that you wanted to resolve. The introduction will also explain if and why your study is new in the subject field and why it is important.

It is often a good idea to wait until the rest of the paper is completed before drafting your introduction. This will help you to stay focused on the manuscript’s important points. The introduction, unlike the abstract, should contain citations to references. The information will help guide your readers through the rest of your document. The key tips for writing an effective introduction :

• Beginning:  The importance of the study.
• Tone/Tense:  Formal, impersonal; present tense.
• Content:  Brief description of manuscript but without results and conclusions.
• Length:  Generally up to four paragraphs. May vary slightly with journal guidelines.

Once you are sure that possible doubts on the difference between the abstract and introduction are clear, review and submit your manuscript.

What struggles have you had in writing an abstract or introduction? Were you able to resolve them? Please share your thoughts with us in the comments section below.

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Really helpful as I prepare to write the introduction to my dissertation. Thank you Enago Academy

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Quite helpful! I’m writing a paper on eyewitness testimony for one of my undergraduate courses at the University of Northern Colorado, and found this to be extremely helpful in clarifications

This was hugely helpful. Keep up the great work!

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I am grateful for the assistance rendered me. I was mystified over the difference between an abstract and introduction during thesis writing. Now I have understood the concept theoretically, I will put that in practice. So thanks a lots it is great help to me.

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• Writing Tips

Abstract vs. Introduction—What’s the Difference?

3-minute read

• 21st February 2022

If you’re a student who’s new to research papers or you’re preparing to write your dissertation , you might be wondering what the difference is between an abstract and an introduction.

Both serve important purposes in a research paper or journal article , but they shouldn’t be confused with each other. We’ve put together this guide to help you tell them apart.

What’s an Introduction?

In an academic context, an introduction is the first section of an essay or research paper. It should provide detailed background information about the study and its significance, as well as the researcher’s hypotheses and aims.

But the introduction shouldn’t discuss the study’s methods or results. There are separate sections for this later in the paper.

An introduction must correctly cite all sources used and should be about four paragraphs long, although the exact length depends on the topic and the style guide used.

What’s an Abstract?

While the introduction is the first section of a research paper, the abstract is a short summary of the entire paper. It should contain enough basic information to allow you to understand the content of the study without having to read the entire paper.

The abstract is especially important if the paper isn’t open access because it allows researchers to sift through many different studies before deciding which one to pay for.

Since the abstract contains only the essentials, it’s usually much shorter than an introduction and normally has a maximum word count of 200–300 words. It also doesn’t contain citations.

The exact layout of an abstract depends on whether it’s structured or unstructured. Unstructured abstracts are usually used in non-scientific disciplines, such as the arts and humanities, and usually consist of a single paragraph.

Structured abstracts, meanwhile, are the most common form of abstract used in scientific papers. They’re divided into different sections, each with its own heading. We’ll take a closer look at structured abstracts below.

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Structuring an Abstract

A structured abstract contains concise information in a clear format with the following headings:

●  Background: Here you’ll find some relevant information about the topic being studied, such as why the study was necessary.

●  Objectives: This section is about the goals the researcher has for the study.

●  Methods: Here you’ll find a summary of how the study was conducted.

●  Results: Under this heading, the results of the study are presented.

●  Conclusions: The abstract ends with the researcher’s conclusions and how the study can inform future research.

Each of these sections, however, should contain less detail than the introduction or other sections of the main paper.

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Abstract vs Introduction – Differences Explained

• By Dr Harry Hothi
• August 29, 2020

Any academic write up of a research study or project will require the inclusion of an abstract and introduction. If you pick up any example of a research paper for a journal, dissertation for a Masters degree or a PhD thesis, you’ll see the abstract, followed by the introduction. At first glance you’ll notice that the abstract is much shorter in length, typically a quarter or third of a page of A4. The introduction on the other hand is longer, taking up at least an entire page of writing.

Beyond the length, what are the differences in the content of the two sections? In short, the abstract is a summary of the entire study, describing the context, research aim, methods, results and key conclusions. The introduction gives more detail on the background of the subject area, the motivation for the study and states the aims and objectives.

Read on to learn more.

What is an Abstract?

The main purpose of an abstract is to succinctly give the reader an overview of why the study was needed, what the purpose of the project was, the research question, the key materials and methods that were used, the main results and what conclusions were drawn from this. Many abstracts also conclude with a sentence on the significance or impact of the research. These are sometimes also referred to as an executive summary.

The reader should have an understanding of the paper topic and what the study was about from the abstract alone. He or she can then decide if they want to read the paper or thesis in more detail.

Abstracts are particularly useful for researchers performing a literature review, which involves critically evaluating a large number of papers. Reading the abstract enables them to quickly ascertain the key points of a paper, helping them identify which ones to read in full.

Abstracts are also very important for learning more about the work performed in papers that are hidden behind academic journal paywalls (i.e. those that are not open access). Abstracts are always made freely available, allowing a researcher to understand the context and main point of the work and then decide if it’s worth paying to read the entire paper. These are sometimes referred to as the ‘de facto introduction’ to the research work as it’s usually the first section people read about your study, after the title page.

How do you Write an Abstract?

The majority of academic journals place a limit of 250 words on the length of the abstract in papers submitted to them. They do this to ensure you give a quick overview of only the most important information from your study, helping the reader decide if they want to read the whole paper too. Make sure you double check the specific requirements of your target journal before you start writing.

Universities or other academic institutions often allow up to 500 words for an abstract written for a doctoral thesis.

Abstracts can be either structured or unstructured in the way they are formatted. A structured abstract contains separate headings to guide the reader through the study. Virtually all STEM journals will require this format be used for a researcharticle. The exact names used for each heading can differ but generally there are defined as:

• Background. This is also sometimes called the Introduction. This section should give an overview of what is currently known about the research topic and what the gap in knowledge is. The reader should understand the problem your research will address; i.e. what was your study needed. Don’t include any references or citations in the abstract.
• Aim and Objective. Give a brief explanation of what the study intended to achieve and state the research question or questions that you proposed. Some authors also include the hypothesis here too.
• Materials and Methods. Use the methods section to describe what you investigated, what the study design was and how you carried it out.
• Results. Give an overview of your key findings.
• Discussion and Conclusion. Some journals may ask for these two terms to be used as separated headings. These sections explain why you may have obtained the results that you did, what this means and what the significance or impact of this might be.

An informative abstract should provide a concise summary of all the important points in your research project, including what the central question relating to the subject matter was. Make it interesting to read too; this may be the difference between your abstract being accepted or rejected if you decide to submit it to an upcoming conference. Reviewers for large conferences often have to read hundreds of abstracts so make sure yours stands out by being easy to read and follow.

It’s less common that you’ll be asked to write an unstructured abstract. If you are, however, be aware that the key difference is that an unstructured abstract does not include separate headings. The flow of the abstract text should still follow the 5 points listed above but they should all be written within one long paragraph.

What is the Introduction?

The introduction section is the first main written work presented after the abstract in your paper manuscript or thesis. In a research paper, the introduction will be followed by a section on the materials and methods. In thesis writing, the introduction will be followed by the literature review .

The main aim of introduction writing is to give the reader more detail on the background information of the study. It should include a brief description of the key current knowledge that exists based on the work presented in previous literature and where the gaps in knowledge are. The introduction should convey why your research was needed in order to add new understanding to your subject area. Make sure that you reference all the publications that you refer to.

When writing an introduction for a scientific paper you should also include the aim of your study and the research objectives/questions. If relevant, also include your hypothesis or (null hypothesis).

How do you Structure the Introduction?

The general rule of thumb for a research paper is to use size 12 Times New Roman font, double spaced. Write four separate paragraphs which together are no longer than one page in length. Structure the four paragraphs as follows:

• Set the context of the research study, giving background information about the subject area.
• Describe what is currently know from previously published work and what is poorly understood – i.e. the research gap.
• Explain how addressing this gap in knowledge is important for your research field – i.e. why this study is needed.
• Give a broad overview of the aims, objectives and hypothesis of the study.

You should not describe the research method used in this section nor any results and conclusions.

You should be clear now on what the differences between an abstract vs introduction are. The best way to improve your academic writing skills for these are to read other examples from other  research articles and start writing!

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Abstract vs. Introduction

What's the difference.

The abstract and introduction are both important sections of a research paper or academic article, but they serve different purposes. The abstract is a concise summary of the entire paper, providing an overview of the research question, methodology, results, and conclusions. It is typically written in a single paragraph and is meant to give readers a quick understanding of the study without having to read the entire paper. On the other hand, the introduction is the first section of the paper and is more detailed. It provides background information on the topic, explains the research problem or question, and outlines the objectives and significance of the study. The introduction sets the stage for the rest of the paper and helps readers understand the context and motivation behind the research.

Further Detail

Introduction.

The introduction is an essential part of any academic or research paper. It serves as the opening section that provides background information, context, and sets the stage for the reader to understand the purpose and significance of the study. The introduction typically includes a thesis statement or research question, outlines the objectives, and highlights the main points that will be discussed in the paper.

One of the primary functions of the introduction is to grab the reader's attention and create interest in the topic. It often begins with a hook or an engaging anecdote to captivate the reader's curiosity. The introduction also provides a brief overview of the existing literature and research related to the topic, highlighting the gaps or limitations that the current study aims to address.

Furthermore, the introduction serves as a roadmap for the rest of the paper, outlining the structure and organization of the subsequent sections. It helps the reader understand the logical flow of the arguments and the overall structure of the paper. The introduction is typically longer than the abstract and provides more detailed information about the research topic.

In summary, the introduction acts as a bridge between the reader and the research paper, providing necessary background information, context, and setting the stage for the study.

The abstract, on the other hand, is a concise summary of the entire research paper. It is usually placed at the beginning of the paper, before the introduction, and provides a brief overview of the study's objectives, methods, results, and conclusions. The abstract aims to give the reader a quick understanding of the research without having to read the entire paper.

Unlike the introduction, the abstract is typically limited to a specific word count or character limit, often ranging from 150 to 300 words. Due to its brevity, the abstract focuses on the most important aspects of the research, highlighting the key findings and their implications. It does not provide an extensive background or literature review like the introduction does.

The abstract is written in a concise and objective manner, using clear and precise language. It avoids unnecessary details, jargon, or technical terms that may confuse the reader. The abstract should be able to stand alone and provide a comprehensive summary of the research, enabling readers to decide whether the paper is relevant to their interests or research.

Overall, the abstract serves as a condensed version of the entire research paper, providing a snapshot of the study's purpose, methods, results, and conclusions. It is designed to give readers a quick overview of the research without delving into the specifics.

While both the abstract and introduction play crucial roles in a research paper, they differ in several key aspects. Let's explore the main differences between these two sections:

1. Length and Detail

The most apparent difference between the abstract and introduction is their length and level of detail. The introduction is typically longer and more detailed, providing a comprehensive background, literature review, and outlining the structure of the paper. It delves into the topic, providing context and setting the stage for the study. On the other hand, the abstract is much shorter and concise, summarizing the key aspects of the research without going into extensive details.

2. Placement

Another significant difference is their placement within the research paper. The introduction is usually the first section after the abstract, serving as the opening of the paper. It provides the necessary background information and context before diving into the main body of the research. In contrast, the abstract is placed at the beginning of the paper, before the introduction, to provide a quick overview of the entire study.

The content of the abstract and introduction also differs. The introduction focuses on providing a comprehensive understanding of the research topic, including the background, literature review, objectives, and main points of the study. It aims to engage the reader and create interest in the research. On the other hand, the abstract summarizes the entire research paper, highlighting the key aspects such as the objectives, methods, results, and conclusions. It aims to give readers a quick understanding of the research without going into extensive details.

4. Audience

The target audience for the abstract and introduction also varies. The abstract is primarily aimed at researchers, scholars, and professionals who want to quickly assess the relevance and significance of the research. It helps them decide whether to read the full paper or not. In contrast, the introduction caters to a broader audience, including those who may not have in-depth knowledge of the subject. It provides the necessary background and context to make the research accessible to a wider range of readers.

Lastly, the abstract and introduction serve different purposes. The introduction aims to provide a comprehensive overview of the research topic, establish the research gap, and present the objectives and main points of the study. It sets the stage for the reader to understand the significance and relevance of the research. On the other hand, the abstract serves as a condensed summary of the entire research paper, allowing readers to quickly grasp the main findings and conclusions without reading the full paper.

In conclusion, while the abstract and introduction are both important sections of a research paper, they serve different purposes and have distinct attributes. The introduction provides a comprehensive background, context, and structure of the research paper, engaging the reader and setting the stage for the study. On the other hand, the abstract offers a concise summary of the entire research, highlighting the key aspects and enabling readers to quickly assess the relevance and significance of the study. Understanding the differences between these sections is crucial for researchers and readers alike to navigate and comprehend research papers effectively.

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Published by Nicolas at March 19th, 2024 , Revised On March 27, 2024

Intro Vs Abstract – Are They The Same?

Scholarly writing serves as a cornerstone for the dissemination of knowledge and the exploration of new ideas. Two crucial elements that play a pivotal role in framing the structure of academic papers are the introduction and abstract. While often used interchangeably, these components serve distinct purposes, each contributing to a scholarly work’s overall coherence and effectiveness.

Table of Contents

Understanding The Introduction

The introduction serves as the gateway to a scholarly work, setting the stage for what lies ahead. It is not merely a perfunctory beginning but a strategic piece that aims to engage readers, provide context, and establish the groundwork for the research to follow. The primary functions of an introduction can be delineated into several key aspects.

Contextualization

The introduction contextualizes the research by presenting the broader field of study. It provides a backdrop against which the specific research question or problem statement can be understood.

This involves reviewing relevant literature, highlighting gaps in existing knowledge, and justifying the need for the current study.

Statement Of The Problem Or Research Question

One of the critical elements of an introduction is the formulation of a clear and concise research question or problem statement. This sets the trajectory for the entire paper, guiding readers on what to expect and why the study is significant.

Objectives And Scope

The introduction outlines the objectives of the research and delineates the scope of the study. This helps readers understand the boundaries within which the research is conducted and what specific aspects will be addressed.

Hypotheses Or Research Hypothesis

In scientific research, the introduction may present hypotheses that the study aims to test. These hypotheses are formulated based on existing knowledge and are critical for guiding the research methodology and analysis.

Thesis Statement

In some academic disciplines, particularly in humanities and social sciences, the introduction may encapsulate the thesis statement —a concise summary of the main argument or position taken in the paper.

Understanding The Abstract

While the introduction sets the stage, the abstract serves as a concise summary that encapsulates the entire research paper. Positioned at the beginning of the paper, the abstract acts as a standalone piece, providing readers with a snapshot of the research without requiring them to delve into the full text. The abstract has its own distinct set of functions and characteristics.

Summary Of Key Elements

The abstract encapsulates the essential elements of the research, including the research question, methodology, key findings, and conclusions. It serves as a condensed version of the entire paper, offering readers a quick overview.

Conciseness And Clarity

Unlike the introduction, the abstract is highly condensed and should be succinct. It demands clarity and precision in conveying the main points of the research without unnecessary details.

A well-crafted abstract can stand alone, providing readers with a clear understanding of the study even if they choose not to read the full paper.

Keywords And Indexing

Abstracts often include keywords that are relevant to the research. These keywords are essential for indexing and categorizing the paper in databases, making it easier for researchers to locate relevant literature.

No Citations Or References

Unlike the introduction, the abstract typically does not include citations or references in APA or MLA to other works. It is a self-contained unit that focuses solely on summarizing the research conducted in the paper.

Structural Alignment

The abstract should mirror the structure of the paper, summarizing each section in a logical sequence. It typically includes brief statements about the introduction, methodology, results, and conclusion.

What Is The Difference Between Intro Vs Abstract

While the introduction and abstract share the common goal of providing readers with a roadmap to the research, they differ significantly in their depth, scope, and functions. Understanding these distinctions is crucial for crafting a well-rounded and impactful research paper.

While an abstract is a tightrope walker, restricted to a concise space, the introduction enjoys the freedom of expansiveness. It can stretch across paragraphs, weaving a tapestry of context and intrigue.

An abstract concentrates on the “what” and the “how” – highlighting the research question, methodology, and results. The introduction delves deeper, exploring the “why” – establishing the importance of your work and engaging the reader emotionally.

An abstract primarily caters to specialists and peer reviewers and needs technical accuracy and jargon. The introduction speaks to a broader audience, using accessible language and captivating storytelling to pique their interest.

An abstract follows a rigid format, typically outlining the research question, methodology, results, and conclusion. The introduction offers greater flexibility, allowing for creative storytelling and engaging transitions.

Depth Of Detail

The introduction provides a comprehensive overview of the background, context, and rationale for the study. It delves into existing literature, establishes the research question, and outlines the objectives. In contrast, the abstract is a condensed summary, offering a snapshot of the entire paper without the depth of detail found in the introduction.

Inclusion Of Citations

The introduction extensively cites relevant literature reviews to provide a foundation for the research. It establishes the scholarly context and justifies the study’s significance. On the other hand, the abstract typically avoids citations and focuses on presenting the research’s key elements without reference to external works.

Readability And Accessibility

The introduction is designed to be read sequentially, guiding readers from the general to the specific. It is an integral part of the paper’s narrative, contributing to the overall flow. In contrast, the abstract is a standalone piece that should be easily understandable on its own. It serves as a quick reference for researchers scanning multiple papers to determine their relevance.

Function Within The Paper

The introduction serves as a foundation for the entire paper, providing the necessary context for readers to understand the study’s purpose and significance.

It invites readers into the research narrative, guiding them through the subsequent sections. On the other hand, the abstract is a succinct summary that allows readers to quickly assess the paper’s content, methodology, and findings without delving into the full text.

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Strategies For Crafting Effective Introductions And Abstracts

Crafting compelling introductions and abstracts is a skill that evolves with practice and a nuanced understanding of the research process. Here are some strategies to enhance the effectiveness of these key components:

Clarity And Precision

Both the introduction and abstract benefit from clarity and precision. Use clear language to convey ideas and avoid unnecessary jargon. Ensure that each sentence serves a specific purpose and contributes to the overall coherence of the text.

Engaging The Reader

The introduction should engage the reader from the outset. Consider using anecdotes, thought-provoking questions, or relevant statistics to capture attention. Create a narrative flow that seamlessly leads readers from the general context to the specific research question.

Conciseness In The Abstract

Given its condensed nature, the abstract requires a careful selection of words to convey maximum information in a limited space. Avoid unnecessary details and focus on presenting the core elements of the research. Aim for brevity without sacrificing clarity.

Both the introduction and abstract should align with the overall structure of the paper. Ensure that the abstract provides a coherent summary of each section, mirroring the paper’s organization. Similarly, the introduction should seamlessly transition into subsequent sections.

Highlighting Significance

Clearly articulate the significance of the research in both the introduction and abstract. Explain why the study is relevant, what gaps it addresses, and how

Proofreading And Editing

Thoroughly proofread and edited both the introduction and abstract to eliminate grammatical errors, typos, and inconsistencies. Pay attention to the overall flow of the text, ensuring that ideas are presented logically and coherently.

Frequently Asked Questions

What is an abstract vs introduction.

An abstract is a concise summary of a research paper, providing an overview of key elements. An introduction contextualizes the study, presents the research question, and outlines objectives, serving as the entry point to the paper.

How to write an abstract vs introduction?

Write a clear, concise abstract by summarizing key research elements: objectives, methodology, findings, and conclusions. Craft an engaging introduction by providing context, stating the research question, and justifying its significance, leading readers into the study seamlessly.

Is introduction and abstract the same?

No, introduction and abstract serve distinct purposes in academic writing. The introduction provides context, states the research question, and justifies the study’s significance. The abstract is a concise summary of the entire paper, presenting key elements independently for quick reference.

Is The introduction on the same page as the abstract?

Yes, in academic papers, the introduction and abstract typically appear on the same page. The abstract precedes the introduction, providing a brief summary of the paper’s key elements, while the introduction introduces the study in more detail on the same page.

What is the difference between abstract and background?

The abstract is a concise summary of a research paper’s key elements. The background provides context in the introduction, detailing the broader field of study, and existing literature, and establishing the foundation for the specific research question or problem.

What is the difference between abstract and overview?

An abstract is a concise summary of a research paper, highlighting key elements. An overview is a broader term, encompassing a brief explanation or review of a subject, topic, or process, providing a general understanding without the depth of detail found in an abstract.

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Abstract vs Introduction: Explaining the Differences and Similarities

by  Antony W

November 14, 2022

Writing a research paper can be challenging because you have to consider so many factors before you start to put words on the paper. You have to choose a research topic, go through the entire research process, create an outline, write your first draft, and proofread your work for coherence, factualness, and clarity.

One area many students don’t seem to get right is on the outline of the paper. Often, they struggle to see a visible difference between an abstract and an introduction, so much so that they confuse the two to mean the same thing. 

Before we go any further, it’s important to understand that an introduction and an abstract for a research paper are not synonymous. They’re different in length, context, writing approach, and the intended purpose.

In this guide, you’ll learn about abstract vs introduction to understand the differences between these two parts of a research paper. In the end, you should find it easy to write a more comprehensive research paper that your instructor will love to read.

Without further ado, let’s get to it.

What is an Abstract in a Research Paper?

An abstract is a section of a research project that gives a reader a condensed version of a research project. Written in past tense, the abstract shows why the study was necessary, the overall purpose of the project, the research question, the materials and methods used, and the drawn conclusions and results. In some cases, an abstract might include an executive summary, which is a conclusive sentence that demonstrates the significance of the research.

The overall goal of an abstract in a research paper is to give a reader the complete summary of the entire project. In fact, by reading this section alone, one should get a clear understanding of the topic and understand the significance of the study.

Abstract are particularly useful because they help with decision-making. After reading the abstract of your research paper, a reader can decide if they want to read the rest of the document for more insights.

What is an Introduction in a Research Paper?

An introduction is the first main section in a research paper. Written immediately after the abstract and before the literature review , the introduction is the part of the project that gives a reader more information on the topic under investigation.

By reading the introduction, a reader should easily understand the knowledge that already exists on the subject and clearly see why your research is necessary for the topic in question. Given that you’re trying to add new understanding to the subject, the aim of your study and research objectives should be very clear.

Where possible, and if indeed necessary, the introduction of the research paper should include a hypothesis. 

Abstract vs Introduction: How Do They Compare?

The comparison table below shows the side-by-side comparison between an abstract and an introduction in a research paper.

Explaining the Differences between an Abstract and an Introduction

There are at least three significant differences between an abstract and an introduction, and it’s important to learn about them before you start writing a research paper.

Abstract vs Introduction: Purpose

The purpose of an abstract is to give your reader a clear, concise summary of the study you conducted on a particular subject. Written in past tense, the abstract is the section that demonstrates whether the paper fits the needs of the reader enough to get them to read other section of the paper. So to grab their attention, pique their interest, and get them to want to continue reading, you should write the abstract in such a manner that it conveys what the paper is about and why it’s important.

An introduction, on the other hand, prepares your reader to discover what you did in your study. It’s in the introduction that you explain:

• Why your study on the subject is important
• Exactly what the study examines
• The studies already conducted in the field

The introduction should also give a summary of what you did in the study.

Abstract vs Introduction: Structure

An abstract doesn’t require the use of subheadings and it’s mostly one block of text. Still, you can structure the abstract such that the information you present flows in a given sequence. You may want to organize your information in the following order:

• The significance of your study
• The basics of your subject
• Questions you’re trying to answer
• How you arrived at your answer and
• The answer to the question

By including this information in their right sequence, you’ll not only be able to give a clear overview of the whole research paper but also give your readers the reasons to keep reading. 

The introduction, on the other hand, may have subheadings to better prepare your reader to understand the study. So you might want to have the following structure overall:

• The importance of the study
• Background information that provides readers with a clear roadmap for the study
• A touch on the previous research that have an impact on the study
• Reasons to investigate the topic even further
• What you intend to do in the study

Structuring your introduction in this manner makes it easy for your readers to care about the study.

Abstract vs Introduction: Length

Many journals require that an abstract be between 200 and 600 words long. For your research paper, you’ll have to make yours at most 350 words, which means you have to write a lot in a small space.

An introduction tends to be longer, often up to 2 pages double-spaced for a normal research article. 

About the author 

Antony W is a professional writer and coach at Help for Assessment. He spends countless hours every day researching and writing great content filled with expert advice on how to write engaging essays, research papers, and assignments.

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Thank you. payment completed., you will receive an email from us to confirm your registration, please click the link in the email to activate your account., there was error during payment, orcid profile found in public registry, download history, structuring your research paper: knowing the difference between abstract, introduction, and conclusion.

• 18 October, 2023

Research papers serve as essential tools in the dissemination of knowledge and the advancement of academic disciplines. Academic papers follow a well-defined structure and format that assists readers in comprehending the content efficiently. They adhere to a well-defined structure and format, which is often referred to as IMRaD: Introduction, Methodology, Results, and Discussion. In addition to these core elements, there are three crucial components; the Abstract, Introduction, and Conclusion, which enhance the deliverance of your research rationale and findings. Understanding the nuanced functions of these sections is crucial for researchers seeking to enhance their paper's clarity, engagement, and influence in the academic and scientific community.

These three components play distinct roles in the structure and communication of a written work, be it a research paper, a thesis, a report, or an article. To write effectively, it's essential to grasp the unique functions and structure of each.

What is an Introduction?

The introduction serves as the opening of your written work, where you set the stage for what is to come. It helps to make the first impression on your readers. Its primary purpose is to provide readers with an overview of the subject matter and the context in which your work exists. 

Furthermore, a well-written introduction outlines the research problem and introduces the main thesis or argument. Some journals may refer to this section as 'Background,' and in others, it might not have a separate heading.

Key elements of an introduction include:

1. Opening Sentence: A compelling hook or opening sentence that grabs the reader's attention and motivates them to continue reading.

2. Thesis Statement: A concise thesis statement that outlines the main argument, purpose, or objective of your work.

3. Background Information: Necessary background information or context to help readers understand the topic.

4. Scope and Significance: A brief discussion of what will be covered and why it is relevant or important.

An introduction should be clear, engaging, and give readers a sense of what to expect. While it provides some insight into the content, it does not delve into the details or findings of the work.

What is an Abstract?

The abstract is a concise summary of the entire document. Its primary purpose is to give readers a quick overview of the key points, methods, findings, and conclusions of the work. They are typically found at the beginning of research papers and articles and are often used by readers to determine whether they want to read the full text. It serves as a preview of the work and helps readers quickly gauge its relevance.

Key elements of an abstract include:

1. Objective: A clear statement of the research objective or purpose.

2. Methods: A brief description of the research methods or approach used.

3. Results: Summary of the key findings or results.

4.  Conclusions: A concise statement of the main conclusions or implications.

These elements are usually presented in a standalone paragraph or a few paragraphs, depending on the specific journal's guidelines.

The length of an abstract varies, often ranging from 150 to 250 words, though it can be longer for some longer papers or theses. Furthermore, it also depends on the style and guidelines of the publication.

Watch this FREE informative webinar to learn more about writing strong abstracts and structuring your research article for publication. 

What is a Conclusion?

The conclusion, as the name suggests, marks the end of your written work. Its primary purpose is to summarize and reiterate the main points and findings discussed in the body of the text. 

Key elements of a conclusion include:

1. Restatement of Thesis: A restatement of the main thesis or argument.

2. Summary of Findings: A brief summary of the key findings and results.

3. Implications: Discussion of the implications of the findings and their significance.

4. Closing Thoughts: A final thought or reflection on the subject matter.

The conclusion is the final part of the paper, summarizing the key findings, their implications, and the main takeaways. In some formats, this section follows the 'Discussion' and may not have a distinct heading.

The conclusion should leave the reader with a sense of closure and a clear understanding of the key takeaways. It is not the place to introduce new information or ideas but rather to reinforce the ideas presented in the body of the work.

What’s the Difference Between Abstract, Introduction, and Conclusion?

To better understand the distinctions and relationships between these three sections, here is a table comparing the features or characteristics of the abstract, introduction, and conclusion for your better understanding:

While these sections serve different functions, it's crucial to avoid repeating the same information. The abstract provides an overview, the introduction sets the stage, and the conclusion wraps up the key points. Repetition can bore readers and waste valuable space. Make each section unique and tailored to its purpose.

The abstract, introduction, and conclusion are the pillars that support the structure and impact of research papers. Understanding their differences and functions is fundamental to effective academic writing. By delving into their relevance, we can uncover their true significance, ensuring that the message of our research reaches its intended audience with clarity and impact. 

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• Key Differences

Know the Differences & Comparisons

Difference Between Abstract and Introduction

On the other hand, the abstract is like a short summary of an academic article or research paper, which discusses the purpose of the study and the outcome of the research. It usually summarizes the research topic, questions, participants, methods, outcome, data collected, analysis and conclusions. The article excerpt given hereunder discusses the difference between abstract and introduction.

Content: Abstract Vs Introduction

Comparison chart, definition of abstract.

An abstract can be described as a concise summary, often found in research work like thesis, dissertations, research articles, review, etc. which helps the reader to have an instant idea of the main purpose of the work. It is about a paragraph long of 150 to 250 words in general.

The information contained in the abstract should be sufficient enough to help the readers judge the nature and importance of the topic, the reasonableness of the strategy used in the investigation, nature of results and conclusions.

An abstract serves a number of purposes such as it allows the readers to get the gist of your paper, so as to decide whether to go through with the rest of the work. It is usually written after the writing of the paperwork is over and that too in the past tense.

An abstract rolls all the important information of the work into a single page, such as the context, general topic, central questions, problem under study, main idea, previous research findings, reasons, research methodology, findings, results, arguments, implications, conclusion and so on. To create an abstract one should pick the main statements from the above-mentioned sections, to draft an abstract.

Types of Abstract

• Descriptive Abstract : It briefly describes the abstract and the length is usually 100-200 words. It indicates the type of information contained in the paper, discusses the purpose of writing, objectives and methods used for research.
• Informative Abstract : As the name suggests, it is a detailed abstract which summarizes all the important points of the study. It includes results and conclusions, along with the purpose, objective, and methods used.

Definition of Introduction

Introduction means to present something to the readers, i.e. by giving a brief description or background information of the document. It is the first and foremost section which expresses the purpose, scope and goals, concerning the topic under study. As an introduction gives an overview of the topic, it develops an understanding of the main text.

An introduction is a gateway to the topic, as it is something which can create interest in the readers to read the document further. It is the crux of the document, which states what is to be discussed in the main body.

Elements of Introduction

An introduction has four basic elements namely: hook, background information, connect and thesis statement.

• Hook is the preliminary sentence of the introduction which is used to fasten the attention of the readers, and so it has to be interesting, attention-grabbing, and readable of course, so as to stimulate the readers to read the complete text.
• Background Information is the main part of the introduction, which presents the background of the research topic, including the problem under study, real-world situation, research questions, and a sneak peek of what the readers can expect from the main body.
• Connect , is a simple line which is used to link or say relate the background information with the research statement, by using words ideas or phrases, so as to ensure the flow and logic of writing the text.
• Thesis statement is the central point of the argument, which is usually a single sentence, whose points of evidence are to be talked about in the following text, i.e. the main body.

Key Differences Between Abstract and Introduction

The difference between abstract and introduction are discussed in the points:

• An abstract is a concise and accurate representation which gives an overview of the main points from the entire document. On the other hand, Introduction is the first section which makes the reader aware of the subject, by giving a brief description of the work, i.e. why the research is needed or important.
• While an abstract will give you an immediate overview of the paper, the introduction is the initial exposure to the subject under study.
• An abstract reports key points of the research, as well as it states why the work is important, what was the main purpose of research, what is the motivation behind choosing the subject, what you learned from the research, what you found out during the research and what you concluded, in a summarized way. As against, an introduction presents a direction to understand what exists in the upcoming portion of the document or book.
• As an abstract has its own introduction, main body and conclusion, it is a standalone document which summarizes the result of the findings and not just the list of topics discussed. As against, the introduction is not a standalone document or piece.
• The main purpose of an abstract is to provide a succinct summary of the research. Conversely, introduction aims at convincing the reader about the need for the research.
• An abstract contains the purpose, problem, methods used, result and conclusion. On the contrary, the introduction includes a hook, background information, connect and thesis statement.
• While abstract is found in a research paper, thesis and dissertations, the introduction is found in a wide range of texts.

An abstract gives a preview of the work, outlines the main points and helps the audience in decision making, i.e. whether they want to read the complete text or not. On the other hand, an introduction is the very first section of the work, which clarifies the purpose of writing.

Without an abstract and introduction, the readers might not be able to know what the work contains and what is the reason or motivation behind the research. So, these two are like thread which goes through the writing and creates an understanding in the reader about the topic under study. While writing these two, one should ensure that they accurately reflect what you cover in the document or book.

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September 20, 2023 at 1:15 am

fantastic explanations

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Abstract vs. Introduction: What is the actual difference?

Published on 07 Dec 2022

If you’ve never written a research paper, the number of boxes to check to complete it can be intimidating. Even if it’s not your first rodeo, there’s still so much to think about that it’s easy to get confused. 

The difference between an abstract and an introduction is a common concern for first-time research writers. 

While these parts may seem similar at first glance, they have distinct characteristics. Whether you’re writing a paper to submit to a journal, an academic conference , or for your MSc or PhD, crafting a good abstract and a unique introduction will save you hassle in the revision stages and increase the likelihood of your paper being accepted. 

What is the Difference Between an Abstract and an Introduction?

In around 250 words, an abstract summarizes the entire study and generates reader interest in your paper. An introduction is the first section of your paper. It covers background information, sets the context for your research, and is longer than an abstract (500 words or more).

The key difference between an abstract and an introduction is their purpose: 

• An abstract is an advertisement. 
• An introduction is a hook.

If you think of an abstract as an advertisement, it should be brief and summarize your paper entirely. People will have to spend their time (maybe even their money) reading your paper. So, your abstract should give them an initial idea of why your paper is relevant to them and what they can expect to learn.

Alternatively, thinking of your introduction as a “hook” means it’s the key to holding the long-term attention of a reader (once they’ve chosen to read your paper). An introduction isn’t about giving all of the research details, it’s about setting the scene for why the details matter.

Beyond purpose, the table below outlines the differences between abstracts and introductions:

Comparison table showing the key differences between an abstract and an introduction.

How to Write a Good Abstract

Your abstract is likely the first thing people will read. It’s a particularly important tool for researchers that have to sort through piles of potential papers to review. 

So, make it clear what your paper is about, why that topic is important, and what you found in your research. Here are 3 tips for writing a good abstract…

1. Consider your abstract format 

There are two basic formats for abstracts. Often, the journal or program you are submitting to will outline what style they expect: 

• A structured abstract includes section headings.
• An unstructured abstract is a single block of text.

Regardless of this structural difference, both of these formats focus on answering the same set of key questions for prospective readers:

• Context/Background: Why is this topic and this research important?
• Objective: What questions are you trying to answer in your research?
• Methods/Design: What are the basic details of your research? In general, how did you go about answering the research questions? 
• Results: What answers did you find? Were there any other observations?
• Conclusion/Takeaways: Were your results expected? Is more research needed?

2. Keep your abstract clear and concise

Your abstract should efficiently deliver information in a way that non-specialists can understand. Detailed descriptions and scientific slang terms don’t belong here. Also, check specific author guidelines to know if there’s a word limit for your abstract (250 words is a common limit).

3. Beat writer’s block by outlining your paper

Just because your abstract is the first thing people will read doesn’t mean it’s the first thing you have to write. It’s helpful to have an outline or loose draft of your entire paper before you write your abstract . Highlight the most important points in each section, then use them to help frame your abstract.

How to Write a Good Introduction

After people have decided to read your paper, it’s your introduction’s time to shine. A good introduction sets the tone for the reader. 

So, make sure that your introduction gives context to your research and makes it clear why your reader should care. Here are 3 tips for writing a great introduction…

1. Answer these questions in your introduction

Some content in your introduction may overlap with your abstract. But, your introduction should cover key questions slightly differently (and in more detail) than your abstract:

• Why is your field of research important?
• What background information is needed to understand your research (include references where applicable)?
• What earlier research impacts the context of your own or helps with understanding your research process?
• How is your research innovative or original?
• What are the sections included in the rest of the paper?

2. Don’t save your introduction for last

“Save your intro for last” is a common tip for various writing applications. But it doesn’t need to be a rule. As Rachael Cayley outlines in this blog post : “You don’t always have to wait until the end to write your introduction. You should review it again of course, but since it's the setup [for the rest of your paper], it’s worth writing first.” 

The introduction shows your reader what led to your research question. So, writing or outlining that part of the story early (and before you forget the details) can help provide accurate context.

3. Consider your introduction’s tone and tense

Use a formal, impersonal tone and speak primarily in the present tense. Double-check the tense used in each sentence or example since there’s a chance you’ll talk about past research in contrast with new processes. Avoid using emotional appeals as they are more suitable for conference presentations and public speaking.

FAQ: Top Abstract and Introduction Questions

Can i use my abstract as my introduction.

The short answer to this question: You shouldn’t. Unless the journal (or your research advisor) asks you to merge your abstract and introduction, it’s best to keep them unique.

Where can I find examples of abstracts and introductions?

This article by Kibin has 10 top-notch abstract examples to get you started. For a step-by-step guide to help you write an introduction, take a look at this article by Scribbr .

How do I write an abstract for an academic conference?

Conference abstract submission is unique. You may still be early in your research process and not have all the results yet. So, the things you include in your abstract will change. Check out our detailed article on writing an abstract for a conference to help you with this.

Apply What You Know About Abstracts and Introductions

Now that you know the key differences between an abstract and an introduction, it’s time to get started writing. If any points for your paper crossed your mind while reading this article, jot them down now to help with making your outline. And be sure to keep in mind: Your abstract is your advertisement. Your introduction is your hook.

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Abstract Vs Introduction: Key Similarities and Differences

Is an abstract the same as an introduction? This is one of the questions we receive most frequently, so we thought it would be a good idea to write an article about the abstract vs introduction problem. Most students don’t know how to differentiate between the two, especially if they are new to academic writing. Even though the two things are somewhat similar, there is at least one major difference between introduction and abstract. In this article, we will discuss the similarities and differences between the two. What is the difference between an abstract and an introduction? Let’s find out!

The Abstract Vs Introduction Problem

Introduction vs abstract: which one does what? Because many professors don’t explain these two terms to their students, it’s easy to confuse them. We consider that this is not the students’ fault. If they don’t know the difference between an abstract and an introduction, it’s easy to make a grave mistake. Of course, you will get penalized harshly for this. This blog post aims to provide information about abstract vs introduction scientific paper writers need to make sure they don’t get an F on their next essay.

Abstract and Introduction: What Are They?

So, let’s discuss abstract vs introduction APA style. An abstract is basically a summary of a complex paper (such as a thesis or a research paper).

The abstract summarizes all the different parts of the paper, including the research problem, the objectives, the methods, the results, and the conclusion. After reading the abstract, the reader should know exactly what the paper is about and how it is structured. The length of an abstract is around 250-300 words. The introduction, on the other hand, is there to give your readers an idea of what you are about to talk about and introduce your thesis statement.

It can contain a bit of background information, but it does not delve into the specifics of your research methods or results. Also, the introduction does not discuss the conclusion of the paper in any way.

The Key Difference Between Abstract and Introduction

OK, but what is the major difference between abstract and introduction? In simple terms, the abstract is a summary of the entire research paper. It briefly discusses the methods, results and conclusion. The introduction, on the other hand, is there to entice the reader to read the entire paper. It discusses just the background of the problem and the objectives of the paper. You will never see the conclusion being discussed in an introduction.

Is an APA abstract vs introduction different from MLA or other types of academic writing? No, the abstract and the introduction are just as different regardless of the academic writing style. You should never confuse one for the other because the consequences can be a rejected paper or at the very least a very low grade.

Introduction vs Abstract: The Similarities

Now that you know the main difference between an abstract and introduction, it’s time to talk about similarities. This should help you avoid any confusion:

• Both the introduction and the abstract are placed at the beginning of a research paper. In fact, an abstract can be considered a de-facto introduction.
• Both the abstract and the introduction are there to provide some information about the subject and about the objectives of your research paper.
• Both can be used as a way to attract the interest of a reader.

However, this is where the similarities end. Never assume that you can write an introduction in place of an abstract. Of course, you can’t write an abstract in place of an introduction either. This is the information about abstract vs introduction lab report writers need to know before they start writing their first paper. We know that sometimes writing an abstract can be more difficult than the introduction to abstract algebra in high school. However, with practice, you will quickly get the hang of it.

Abstract and Introduction Examples

To help you understand the meaning and role of an abstract better, we have written an example abstract for you and broken it down into pieces:

As of 2023, residual herbicide that is accumulating in certain crops is posing a growing threat to the rice-wheat rotation in northern India. (The background part) When it comes to pesticides and pesticide metabolites, green manure has been shown to stimulate ample co-mineralization. By incorporating it into the soil, the effects of the herbicide residue can be mitigated. (The objectives part) During a three-year study at the North Indian Wheat Research Institute, Azolla Pinata and A. Carolingiana have been used as green manure. The effects of the green manure on the Propanil and Buthachlor herbicides has been evaluated, as well as the mineralization and co-metabolization of the herbicides, using a process known as liquid chromatography. (The material and methods part) Initial results indicate that Azolla Pinata caused the Propanil herbicide to co-mineralize in 14 days. However, the green manure did not have the intended effect on the Buthachlor herbicide during the study. (The findings part) After analyzing the findings of the study, we can say for certain that Azolla Pinata used as green manure can prevent residual Propanil accumulation. (The conclusion part)

An example introduction for the paper would look something like this:

Residual herbicides are posing a growing threat to the systems of rice-wheat rotation in Northern India. According to a recent study by the North Indian Wheat Research Institute, Azolla Pinata is able to co-mineralize some herbicides. Understanding the process by which this happens is important for the future of Indian rice and wheat crops. This research paper aims to answer the following question: how does green manure co-mineralize certain herbicides? We will first analyze the soil and the herbicide accumulation, then we will discuss the effects of green manure, and finally we will analyze the potential applications.

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How to Write a Research Paper Introduction (with Examples)

The research paper introduction section, along with the Title and Abstract, can be considered the face of any research paper. The following article is intended to guide you in organizing and writing the research paper introduction for a quality academic article or dissertation.

The research paper introduction aims to present the topic to the reader. A study will only be accepted for publishing if you can ascertain that the available literature cannot answer your research question. So it is important to ensure that you have read important studies on that particular topic, especially those within the last five to ten years, and that they are properly referenced in this section. 1 What should be included in the research paper introduction is decided by what you want to tell readers about the reason behind the research and how you plan to fill the knowledge gap. The best research paper introduction provides a systemic review of existing work and demonstrates additional work that needs to be done. It needs to be brief, captivating, and well-referenced; a well-drafted research paper introduction will help the researcher win half the battle.

The introduction for a research paper is where you set up your topic and approach for the reader. It has several key goals:

• Present your research topic
• Capture reader interest
• Summarize existing research
• Position your own approach
• Define your specific research problem and problem statement
• Highlight the novelty and contributions of the study
• Give an overview of the paper’s structure

The research paper introduction can vary in size and structure depending on whether your paper presents the results of original empirical research or is a review paper. Some research paper introduction examples are only half a page while others are a few pages long. In many cases, the introduction will be shorter than all of the other sections of your paper; its length depends on the size of your paper as a whole.

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Table of Contents

What is the introduction for a research paper, why is the introduction important in a research paper, craft a compelling introduction section with paperpal. try now, 1. introduce the research topic:, 2. determine a research niche:, 3. place your research within the research niche:, craft accurate research paper introductions with paperpal. start writing now, frequently asked questions on research paper introduction, key points to remember.

The introduction in a research paper is placed at the beginning to guide the reader from a broad subject area to the specific topic that your research addresses. They present the following information to the reader

• Scope: The topic covered in the research paper
• Context: Background of your topic
• Importance: Why your research matters in that particular area of research and the industry problem that can be targeted

The research paper introduction conveys a lot of information and can be considered an essential roadmap for the rest of your paper. A good introduction for a research paper is important for the following reasons:

• It stimulates your reader’s interest: A good introduction section can make your readers want to read your paper by capturing their interest. It informs the reader what they are going to learn and helps determine if the topic is of interest to them.
• It helps the reader understand the research background: Without a clear introduction, your readers may feel confused and even struggle when reading your paper. A good research paper introduction will prepare them for the in-depth research to come. It provides you the opportunity to engage with the readers and demonstrate your knowledge and authority on the specific topic.
• It explains why your research paper is worth reading: Your introduction can convey a lot of information to your readers. It introduces the topic, why the topic is important, and how you plan to proceed with your research.
• It helps guide the reader through the rest of the paper: The research paper introduction gives the reader a sense of the nature of the information that will support your arguments and the general organization of the paragraphs that will follow. It offers an overview of what to expect when reading the main body of your paper.

What are the parts of introduction in the research?

A good research paper introduction section should comprise three main elements: 2

• What is known: This sets the stage for your research. It informs the readers of what is known on the subject.
• What is lacking: This is aimed at justifying the reason for carrying out your research. This could involve investigating a new concept or method or building upon previous research.
• What you aim to do: This part briefly states the objectives of your research and its major contributions. Your detailed hypothesis will also form a part of this section.

How to write a research paper introduction?

The first step in writing the research paper introduction is to inform the reader what your topic is and why it’s interesting or important. This is generally accomplished with a strong opening statement. The second step involves establishing the kinds of research that have been done and ending with limitations or gaps in the research that you intend to address. Finally, the research paper introduction clarifies how your own research fits in and what problem it addresses. If your research involved testing hypotheses, these should be stated along with your research question. The hypothesis should be presented in the past tense since it will have been tested by the time you are writing the research paper introduction.

The following key points, with examples, can guide you when writing the research paper introduction section:

• Highlight the importance of the research field or topic
• Describe the background of the topic
• Present an overview of current research on the topic

Example: The inclusion of experiential and competency-based learning has benefitted electronics engineering education. Industry partnerships provide an excellent alternative for students wanting to engage in solving real-world challenges. Industry-academia participation has grown in recent years due to the need for skilled engineers with practical training and specialized expertise. However, from the educational perspective, many activities are needed to incorporate sustainable development goals into the university curricula and consolidate learning innovation in universities.

• Reveal a gap in existing research or oppose an existing assumption
• Formulate the research question

Example: There have been plausible efforts to integrate educational activities in higher education electronics engineering programs. However, very few studies have considered using educational research methods for performance evaluation of competency-based higher engineering education, with a focus on technical and or transversal skills. To remedy the current need for evaluating competencies in STEM fields and providing sustainable development goals in engineering education, in this study, a comparison was drawn between study groups without and with industry partners.

• State the purpose of your study
• Highlight the key characteristics of your study
• Describe important results
• Highlight the novelty of the study.
• Offer a brief overview of the structure of the paper.

Example: The study evaluates the main competency needed in the applied electronics course, which is a fundamental core subject for many electronics engineering undergraduate programs. We compared two groups, without and with an industrial partner, that offered real-world projects to solve during the semester. This comparison can help determine significant differences in both groups in terms of developing subject competency and achieving sustainable development goals.

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You can use the same process to develop each section of your article, and finally your research paper in half the time and without any of the stress.

The purpose of the research paper introduction is to introduce the reader to the problem definition, justify the need for the study, and describe the main theme of the study. The aim is to gain the reader’s attention by providing them with necessary background information and establishing the main purpose and direction of the research.

The length of the research paper introduction can vary across journals and disciplines. While there are no strict word limits for writing the research paper introduction, an ideal length would be one page, with a maximum of 400 words over 1-4 paragraphs. Generally, it is one of the shorter sections of the paper as the reader is assumed to have at least a reasonable knowledge about the topic. 2 For example, for a study evaluating the role of building design in ensuring fire safety, there is no need to discuss definitions and nature of fire in the introduction; you could start by commenting upon the existing practices for fire safety and how your study will add to the existing knowledge and practice.

When deciding what to include in the research paper introduction, the rest of the paper should also be considered. The aim is to introduce the reader smoothly to the topic and facilitate an easy read without much dependency on external sources. 3 Below is a list of elements you can include to prepare a research paper introduction outline and follow it when you are writing the research paper introduction. Topic introduction: This can include key definitions and a brief history of the topic. Research context and background: Offer the readers some general information and then narrow it down to specific aspects. Details of the research you conducted: A brief literature review can be included to support your arguments or line of thought. Rationale for the study: This establishes the relevance of your study and establishes its importance. Importance of your research: The main contributions are highlighted to help establish the novelty of your study Research hypothesis: Introduce your research question and propose an expected outcome. Organization of the paper: Include a short paragraph of 3-4 sentences that highlights your plan for the entire paper

Cite only works that are most relevant to your topic; as a general rule, you can include one to three. Note that readers want to see evidence of original thinking. So it is better to avoid using too many references as it does not leave much room for your personal standpoint to shine through. Citations in your research paper introduction support the key points, and the number of citations depend on the subject matter and the point discussed. If the research paper introduction is too long or overflowing with citations, it is better to cite a few review articles rather than the individual articles summarized in the review. A good point to remember when citing research papers in the introduction section is to include at least one-third of the references in the introduction.

The literature review plays a significant role in the research paper introduction section. A good literature review accomplishes the following: Introduces the topic – Establishes the study’s significance – Provides an overview of the relevant literature – Provides context for the study using literature – Identifies knowledge gaps However, remember to avoid making the following mistakes when writing a research paper introduction: Do not use studies from the literature review to aggressively support your research Avoid direct quoting Do not allow literature review to be the focus of this section. Instead, the literature review should only aid in setting a foundation for the manuscript.

Remember the following key points for writing a good research paper introduction: 4

• Avoid stuffing too much general information: Avoid including what an average reader would know and include only that information related to the problem being addressed in the research paper introduction. For example, when describing a comparative study of non-traditional methods for mechanical design optimization, information related to the traditional methods and differences between traditional and non-traditional methods would not be relevant. In this case, the introduction for the research paper should begin with the state-of-the-art non-traditional methods and methods to evaluate the efficiency of newly developed algorithms.
• Avoid packing too many references: Cite only the required works in your research paper introduction. The other works can be included in the discussion section to strengthen your findings.
• Avoid extensive criticism of previous studies: Avoid being overly critical of earlier studies while setting the rationale for your study. A better place for this would be the Discussion section, where you can highlight the advantages of your method.
• Avoid describing conclusions of the study: When writing a research paper introduction remember not to include the findings of your study. The aim is to let the readers know what question is being answered. The actual answer should only be given in the Results and Discussion section.

To summarize, the research paper introduction section should be brief yet informative. It should convince the reader the need to conduct the study and motivate him to read further. If you’re feeling stuck or unsure, choose trusted AI academic writing assistants like Paperpal to effortlessly craft your research paper introduction and other sections of your research article.

1. Jawaid, S. A., & Jawaid, M. (2019). How to write introduction and discussion. Saudi Journal of Anaesthesia, 13(Suppl 1), S18.

2. Dewan, P., & Gupta, P. (2016). Writing the title, abstract and introduction: Looks matter!. Indian pediatrics, 53, 235-241.

3. Cetin, S., & Hackam, D. J. (2005). An approach to the writing of a scientific Manuscript1. Journal of Surgical Research, 128(2), 165-167.

4. Bavdekar, S. B. (2015). Writing introduction: Laying the foundations of a research paper. Journal of the Association of Physicians of India, 63(7), 44-6.

Paperpal is a comprehensive AI writing toolkit that helps students and researchers achieve 2x the writing in half the time. It leverages 21+ years of STM experience and insights from millions of research articles to provide in-depth academic writing, language editing, and submission readiness support to help you write better, faster.  

Get accurate academic translations, rewriting support, grammar checks, vocabulary suggestions, and generative AI assistance that delivers human precision at machine speed. Try for free or upgrade to Paperpal Prime starting at US$19 a month to access premium features, including consistency, plagiarism, and 30+ submission readiness checks to help you succeed.  

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Open Access

Peer-reviewed

Research Article

Cardiovascular health and cancer risk associated with plant based diets: An umbrella review

Roles Conceptualization, Data curation, Formal analysis, Writing – original draft

Affiliations Department of Biomedical and Neuromotor Science, Alma Mater Studiorum–University of Bologna, Bologna, Italy, Interdisciplinary Research Center for Health Science, Sant’Anna School of Advanced Studies, Pisa, Tuscany, Italy

Roles Conceptualization, Formal analysis, Writing – review & editing

Affiliation Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom

Roles Conceptualization, Methodology, Supervision, Writing – original draft, Writing – review & editing

* E-mail: [email protected]

Affiliation Department of Biomedical and Neuromotor Science, Alma Mater Studiorum–University of Bologna, Bologna, Italy

Roles Conceptualization, Supervision, Writing – review & editing

Affiliation Stanford Prevention Research Center, Stanford University School of Medicine, Stanford, CA, United States of America

Affiliation Department of Translational Medicine, University of Eastern Piedmont, (UNIUPO), Novara, Italy

Roles Conceptualization, Data curation, Writing – review & editing

Roles Conceptualization, Methodology, Supervision, Writing – review & editing

Affiliation IRCCS Istituto delle Scienze Neurologiche di Bologna, Programma Neurochirurgia Ipofisi—Pituitary Unit, Bologna, Italy

• Angelo Capodici, 
• Gabriele Mocciaro, 
• Davide Gori, 
• Matthew J. Landry, 
• Alice Masini, 
• Francesco Sanmarchi, 
• Matteo Fiore, 
• Angela Andrea Coa, 
• Gisele Castagna, 

• Published: May 15, 2024
• https://doi.org/10.1371/journal.pone.0300711
• Reader Comments

Cardiovascular diseases (CVDs) and cancer are the two main leading causes of death and disability worldwide. Suboptimal diet, poor in vegetables, fruits, legumes and whole grain, and rich in processed and red meat, refined grains, and added sugars, is a primary modifiable risk factor. Based on health, economic and ethical concerns, plant-based diets have progressively widespread worldwide.

This umbrella review aims at assessing the impact of animal-free and animal-products-free diets (A/APFDs) on the risk factors associated with the development of cardiometabolic diseases, cancer and their related mortalities.

Data sources

PubMed and Scopus were searched for reviews, systematic reviews, and meta-analyses published from 1st January 2000 to 31st June 2023, written in English and involving human subjects of all ages. Primary studies and reviews/meta-analyses based on interventional trials which used A/APFDs as a therapy for people with metabolic diseases were excluded.

Data extraction

The umbrella review approach was applied for data extraction and analysis. The revised AMSTAR-R 11-item tool was applied to assess the quality of reviews/meta-analyses.

Overall, vegetarian and vegan diets are significantly associated with better lipid profile, glycemic control, body weight/BMI, inflammation, and lower risk of ischemic heart disease and cancer. Vegetarian diet is also associated with lower mortality from CVDs. On the other hand, no difference in the risk of developing gestational diabetes and hypertension were reported in pregnant women following vegetarian diets. Study quality was average. A key limitation is represented by the high heterogeneity of the study population in terms of sample size, demography, geographical origin, dietary patterns, and other lifestyle confounders.

Conclusions

Plant-based diets appear beneficial in reducing cardiometabolic risk factors, as well as CVDs, cancer risk and mortality. However, caution should be paid before broadly suggesting the adoption of A/AFPDs since the strength-of-evidence of study results is significantly limited by the large study heterogeneity alongside the potential risks associated with potentially restrictive regimens.

Citation: Capodici A, Mocciaro G, Gori D, Landry MJ, Masini A, Sanmarchi F, et al. (2024) Cardiovascular health and cancer risk associated with plant based diets: An umbrella review. PLoS ONE 19(5): e0300711. https://doi.org/10.1371/journal.pone.0300711

Editor: Melissa Orlandin Premaor, Federal University of Minas Gerais: Universidade Federal de Minas Gerais, BRAZIL

Received: January 8, 2024; Accepted: March 4, 2024; Published: May 15, 2024

Copyright: © 2024 Capodici et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the paper and its Supporting Information files.

Funding: The author(s) received no specific funding for this work.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Cardiovascular diseases (CVDs) and cancer currently represent the leading causes of death and disability worldwide. Studies performed on large cohorts worldwide have identified several modifiable and non-modifiable risk factors. Among them, robust evidence supports diet as a major modifiable risk factor [ 1 ].

A suboptimal diet, marked by insufficient consumption of fruits, vegetables, legumes, and whole grains, coupled with an excessive intake of meat (particularly red and processed), salt, refined grains and sugar, has been shown to notably elevate both mortality rates and disability-adjusted life years. Over time, these dietary choices have led to a concerning increase in health-related issues [ 1 , 2 ].

Additionally, the reduction of products of animal origin in favor of vegetarian ones has been suggested to reduce CVD and cancer risk [ 3 , 4 ]. Several major professional and scientific organizations encourage the adoption of vegetarian and vegan diets for the prevention and treatment of a range of chronic metabolic diseases such as atherosclerosis, type 2 diabetes, hypertension and obesity [ 5 , 6 ]. Ethical, environmental, and socio-economic concerns have contributed to the widespread growth of plant-based diets, particularly vegetarian and vegan options [ 7 – 9 ]. 2014 cross-national governmental survey estimated that approximately 75 million people around the globe deliberately followed a vegetarian diet, while an additional 1,45 million were obliged to because of socio-economic factors [ 10 , 11 ].

At the same time, study heterogeneity in terms of plant-based dietary regimens (from limitation of certain types to the total exclusion of animal products), their association with other lifestyle factors, patient demographic and geographical features, associated diseases, as well as study design and duration, significantly limit the assessment of the real benefits associated with animal-free and animal-products-free diets (A/APFDs). Finally, an increasing number of studies have highlighted the potential threatening consequences of chronic vitamin and mineral deficiencies induced by these diets (e.g., megaloblastic anemia due to vitamin B12 deficiency), especially more restrictive ones and in critical periods of life, like pregnancy and early childhood [ 5 ].

Based on these premises, our umbrella review aims at assessing the impact of animal-free and animal-products-free diets (A/APFDs) on the risk factors associated with the development of cardiometabolic diseases, cancer and their related mortalities in both the adult and the pediatric population, as well as pregnant women.

Search strategy

PubMed ( https://pubmed.ncbi.nlm.nih.gov/ ) and Scopus ( https://www.scopus.com/search/form.uri?display=basic#basic ) databases were searched for reviews, systematic reviews and meta-analyses published from 1st January 2000 to 31st June 2023. We considered only articles written in English, involving human subjects, with an available abstract, and answering to the following PICO question: P (population): people of all ages; I (intervention) and C (comparison): people adopting A/APFDs vs. omnivores; O (outcome): impact of A/APFD on health parameters associated with CVDs, metabolic disorders or cancer.

Articles not specifying the type of A/APFD regimen were excluded. If not detailed, the A/APFDs adopted by study participants was defined as “mixed diet”. Vegetarian diets limiting but not completely excluding certain types of meat/fish (i.e. pesco- or pollo-vegetarian diet) were excluded. Studies focusing on subjects with specific nutritional needs (i.e., athletes or military personnel) -except pregnant women-, or with known underlying chronic diseases (i.e., chronic kidney disease), as well as articles focusing on conditions/health parameters related to disorders different from CVDs or cancer, and, finally, reviews/meta-analyses including interventional studies assessing A/APFDs comparing it with pharmacological interventions were excluded.

Ad hoc literature search strings, made of a broad selection of terms related to A/APFDs, including PubMed MeSH-terms, free-text words and their combinations, combined by proper Boolean operators, were created to search PubMed database: ((vegetari* OR vegan OR Diet , Vegetarian[MH] OR fruitar* OR veganism OR raw-food* OR lacto-veget* OR ovo-vege* OR semi-veget* OR plant-based diet* OR vegetable-based diet* OR fruit-based diet* OR root-based diet OR juice-based diet OR non-meat eate* OR non-meat diet*) AND ((review[Publication Type]) OR (meta-analysis[Publication Type]))) AND (("2000/01/01"[Date—Publication] : "2023/06/31"[Date—Publication])) and Scopus database: ALL(vegetari* OR vegan OR Diet , Vegetarian OR fruitar* OR veganism OR raw-food* OR lacto-veget* OR ovo-vege* OR semi-veget* OR plant-based diet* OR vegetable-based diet* OR fruit-based diet* OR root-based diet OR juice-based diet OR non-meat eate* OR non-meat diet) AND SUBJAREA(MEDI OR NURS OR VETE OR DENT OR HEAL OR MULT) PUBYEAR > 1999 AND (LIMIT-TO (DOCTYPE , "re"))

Research design and study classification

An umbrella review approach [ 12 ] was applied to systematically assess the effect of A/APFDs on risk factors related to CVDs, metabolic disorders and cancer as derived from literature reviews, systematic reviews and meta-analyses ( Table 1 ).

• PPT PowerPoint slide
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• TIFF original image

https://doi.org/10.1371/journal.pone.0300711.t001

Study selection

The list of articles identified by literature search was split into 5 equivalent parts, each assigned to a couple of readers (AC, DG, CW, ML, AM, FS, MF, AAC, GC and FG), who independently and blindly read the title and then the abstract of each article to define its pertinence. Papers included in the umbrella review had to focus on one/some of the following A/APFDs: vegans, lacto-vegetarians, ovo-vegetarians, lacto-ovo-vegetarians. No restriction was applied for age, gender, ethnicity, geographical origin, nor socio economic status. Primary studies, reviews/meta-analyses not written in English, or focusing on non-previously mentioned dietary regimens (including the Mediterranean diet) were excluded. Abstract meetings, editorials, letters to the editor, and study protocols were also excluded. To reduce study heterogeneity, at least in terms of dietary regimens, we excluded studies based on vegetarian regimens limiting but not avoiding fish or poultry, and prospective trials directly comparing A/AFPDs to pharmacological interventions.

In case of discordance between readers, we resorted to discussion amongst the authors to resolve it, based on the article’s abstract or, if not decisive, the full text. The study selection process is summarized in Fig 1 .

https://doi.org/10.1371/journal.pone.0300711.g001

This review was registered on PROSPERO (Record ID: 372913 https://www.crd.york.ac.uk /prospero/display_record.php?RecordID=372913 ).

Quality literature analysis

Three raters (AC, DG, FS) independently and blindly assessed the quality of the systematic reviews and meta-analyses using the revised AMSTAR-R 11-item tool, developed by the PEROSH group [ 13 ]. In case of disagreement, the score of each item and the final decision were discussed among the three raters.

Data extraction and reporting

Ten investigators (AC, DG, GM, ML, AM, FS, MF, AAC, GC, FG) independently extracted data from eligible articles. Disagreements in data extraction were resolved by consensus. Using a predefined protocol and a Microsoft Excel sheet, the following data were extracted: first author’s affiliation country; type of review; type of diet; target population; number of aggregated participants; total cholesterol; HDL-cholesterol; LDL-cholesterol; triglycerides; apolipoprotein B; C-Reactive Protein (CRP); Body Mass Index (BMI); body weight; fasting glucose; glycosylated hemoglobin (HbA1c); systolic blood pressure; diastolic blood pressure; cardiac events (type; risk); cardiovascular diseases (type; risk); gestational diabetes; gestational hypertension; cancer (type; risk); death due to CVDs/cancer (risk). Data were reported as mean difference (MD), weighted mean difference (WMD), standardized mean difference (SMD), and 95%CI, while the estimated risk could be reported as relative risk (RR), odds ratio (OR), or hazard ratio (HR), according to the data reported by the study authors. Articles assessing the risk of gestational diabetes and hypertension, as well as risk of low birth weight, and their determinants were examined separately.

Results from studies focusing on both vegetarian and vegan diets were analyzed and reported separately if authors had stratified the results according to the type of diet. On the contrary, if data from vegan and vegetarian subjects were mixed, we arbitrarily considered all of them as “vegetarian”.

Group 1: Cardiovascular endpoints and risk factors

I. total cholesterol (tc)..

Eight studies examined the levels of total serum cholesterol (TC) in vegetarians. Two focused on the general population and included 5,561 [ 14 ] and 576 [ 15 ] respectively, and, based on data meta-analysis, found a significant reduction in TC among vegetarians and people who assumed plant-based proteins (MD: -1.56 mmol/L; 95%CI: −1.73, −1.39; and -0.11 mmol/L; 95%CI: −0.22, −0.01, respectively).

Data were confirmed by Wang et al. (N = 832 total; Ovolacto/lacto-vegetarians: 291) [ 16 ], showing a greater dietary effect in subjects with a BMI ranging from 18.5 to 25 kg/m 2 (mean TC reduction: −0.94 mmol/L; 95%CI: −1.33, −0.55), and from 25 to 30 kg/m 2 (−0.58 mmol/L; 95%CI: −0.89, −0.27), than in those with a BMI >30 kg/m 2 (−0.16 mmol/L; 95%CI: −0.30, −0.01), and by Xu et al. (N = 783) [ 17 ], reporting lower TC in overweight and obese people (WMD: −0.37 mmol/L; 95%CI: −0.52, −0.22) adopting a vegetarian diet.

Another systematic review by Elliott et al., including 27 randomized controlled trials on plant based vs. normal western diets [ 18 ], found lower TC levels in vegetarians. These results were in line with other two descriptive reviews, the first including 2,890 overweight/obese adults [ 19 ], the second 8,969 vegetarian children aged 0–18 years [ 20 ]. Furthermore, a meta-analysis by Liang et al. described significantly lower TC (from -0.36 to -0.24 mmol/L) in people adopting plant based diets vs. people adopting western habitual diets [ 21 ].

Moreover, the review and meta-analysis by Dinu et al. [ 14 ], based on 19 studies for a total of 1,272 adults, reported significantly lower levels of TC among vegans than in omnivores (WMD: −1.72 mmol/L; 95%CI: −1.93, −1.51).

II. High-density lipoprotein cholesterol (HDL-C).

Eight reviews focused on the effects of vegetarian diet on serum high-density lipoprotein cholesterol (HDL-C) levels. Six [ 15 , 17 , 18 , 21 – 23 ] found no significant difference between vegetarians and omnivores, when considering normal weight and overweight/obese people. On the contrary, the study by Dinu et al. [ 14 ], based on 51 studies, for a total of 6,194 vegetarian adults, reported a WMD −0.15 mmol/L (95%CI: −0.19, −0.11). Liang et al. [ 21 ] analyzed 4 studies and reported a pooled estimated MD of −0.10 mmol/L (95%CI: −0.14, −0.05; p<0.001) in vegetarian diet adopters vs. western diets adopters. Finally, Zhang et al. [ 22 ] did not find any statistically significant differences in HDL-C levels when assessing vegetarian diets compared to non-vegetarians; on the same note Dinu et al. [ 14 ], analyzing data from 15 studies, for a total of 1,175 adults, found no significant differences in HDL-C levels between vegans and people following other dietary regimens.

III. Low-density lipoprotein cholesterol (LDL-C).

Ten reviews summarized the effect of vegetarian diets on serum levels of low-density lipoprotein cholesterol (LDL-C). Seven [ 14 – 18 , 21 , 23 ] found significantly lower LDL-C levels associated with vegetarian diet, both in the general population and in diabetic patients. In particular, Elliot et al. [ 18 ], analyzing 43 observational and interventional studies, described lower LDL-C in people adopting plant based diets; a significant difference was reported by the study of Liang et al. [ 21 ] based on 68 studies (MD: -0.29 to -0.17), and similar to data by Lamberg et al. [ 15 ], based on 13 RCTs including for a total of 576 participants (MD: -0.14 mmol/L; 95%CI: -0.25, -0.02). The impact of vegetarian diet appeared even greater in overweight or obese people, according to the analysis by Xu et al. [ 17 ], based on 7 RCTs (N = 783; MD: -0.31 mmol/L; 95%CI: -0.46, -0.16). Two reviews [ 19 , 20 ] reported similar results in overweight/obese patients and children aged 0–18 years, but no meta-analyses were conducted. Wang et al. [ 16 ] reported a MD of −0.34 mmol/L (95%CI: −0.57, −0.11; p<0.001) in the general adult population. Ferdowsian et al. [ 23 ] reported an overall reduction of LDL-C associated with vegetarian diet, but no synthesis analyses were performed. Dinu et al. [ 14 ] analyzed 46 studies encompassing 5,583 vegetarians and found a WMD of -1.18 mmol/L (95%CI: -1.34, -1.01). Finally, Viguiliouk et al. [ 24 ] reported a MD of −0.12 mmol/L (95%CI: −0.20, −0.04) in 6 trials involving 602 diabetic patients.

Four reviews identified a significant reduction in LDL-C in vegans as compared to omnivores [ 14 , 19 , 23 , 25 ]. Benatar et al. [ 25 ] analyzed 31 studies, for a total of 3,355 healthy vegan adults and 53,393 non-vegan controls and found MD of -0.49 mmol/L (95%CI: -0.62, -0.36; p<0.0001). Ferdowsian et al. [ 23 ] reported a reduction of LDL-C in healthy vegans, and Ivanova et al. [ 19 ] in overweight patients, but no meta-analysis was performed. Finally, Dinu et al. [ 14 ] analyzed 13 studies, for a total of 728 healthy vegan adults, and found a significant LDL-C reduction (WMD: −1.27 mmol/L; 95%CI: −1.66, −0.88).

IV. Triglycerides (TG).

Seven systematic reviews [ 14 , 16 – 18 , 20 , 23 , 26 ] analyzed serum triglycerides (TG) in vegetarians vs. omnivores. Specifically, Wang et al. [ 16 ] described no differences between the two, with a pooled estimated effect of 0.04 mmol/L (95%CI: −0.05, 0.13; p = 0.4). Zhang et al. [ 26 ] analyzing 12 studies for a total of 1,300 subjects, found a MD of −1.28 mmol/L (95%CI; −2.14, −0.42). Schürmann et al. and Ferdowsian et al. [ 20 , 23 ] reported lower TG in vegetarians in both children and adults but did not perform data meta-analysis. Dinu et al. [ 14 ] analyzed 55 studies including 4,008 vegetarians and found a WMD of −0.63 mmol/L (95%CI: −0.97, −0.30; p = 0.02). Conversely, in the review by Elliott et al. [ 18 ] no differences were reported in triglycerides. Xu et al. [ 17 ] reported a significant increase of TG (WMD: 0.29 mmol/L; 95%CI: 0.11, 0.47) in vegetarians as compared to meat eaters.

The effect of vegan diet on TG remains debated as one review [ 23 ] reported significative changes in TGs (-0.14 mmol/L, CI -0.24 to -0.05), while another [ 14 ] did not find any differences between vegans and omnivores since, after having analyzed 13 studies for 483 vegans, they reported a WMD of -0.52 mmol/L (95%CI: -1.13; 0.09).

V. C-reactive protein (CRP).

Three studies reported lower C-reactive protein (CRP) levels in normal weight, overweight and obese vegetarians as compared to non-vegetarians. Craddock et al. and Menzel et al. reported a WMD of -0.61 mg/L (95%CI: -0.91, -0.32; p = 0.0001) [ 27 ]; -0.25 mg/L (95%CI: -0.49, 0; p = 0.05) [ 28 ], respectively.

Data derived from the analysis by Menzel et al. [ 28 ] in vegan subjects were in line with previously mentioned studies performed in vegetarians (WMD: -0.54 mg/L; 95%CI: -0.79, -0.28; p<0.0001).

Two reviews [ 29 , 30 ] focused on the effects of mixed vegetarian diets on CRP levels. The first [ 29 ] included 2,689 obese patients and found a WMD of -0.55 mg/L (95%CI: -0.78, -0.32; I 2 = 94.4%), while the other [ 30 ], based on 2,398 normal weight subjects found no significant differences between vegetarians and omnivores in the primary analysis; alas, when considering a minimum duration of two years vegetarianism they described lower CRP levels vs. omnivores (Hedges’ g = -0.29; 95%CI: -0.59, 0.01).

VI. Plant-based diets and lipids.

Three studies [ 23 , 26 , 31 ] assessed the lipid profile in people following plant-based diets (without differentiating among diet subtypes) in comparison with omnivores. All of them found significantly lower levels of TC, HDL-C and LDL-C in subjects following plant-based diets. Specifically, Yokoyama et al. [ 31 ] reported a WMD of −1.62 mmol/L (95%CI: −1.92, −1.32; p< 0.001; I 2 = 81.4) for TC, −1.27 mmol/L (95%CI: −1.55, −0.99; p< 0.001; I 2 = 83.3) for LDL-C, −0.2 mmol/L (95%CI: −0.26, −0.14; p< 0.001; I 2 = 49.7) for HDL-C, and −0.36 mmol/L; 95%CI: −0.78, 0.06; p = 0.092; I 2 = 83.0) for TG when considering observational studies, and of −0.69 mmol/L (95%CI: −0.99, −0.4; p<0.001; I 2 = 54.8) for TC, −0.69 mmol/L (95%CI: −0.98, −0.37; p<0.001; I 2 = 79.2) for LDL-C, −0.19 mmol/L (95%CI: −0.24, −0.14; p<0.001; I 2 = 8.5) for HDL-C, and a non-statistically significant increase of TG based on prospective cohort studies. Additionally, Zhang et al. [ 26 ] in their meta-analysis, including 1,300 subjects, found a SMD of -1.28 mmol/L in TG (95% CI -2.14 to -0.42).

Finally, Picasso et al. [ 32 ] did not find any differences in triglycerides for mixed vegetarian diets (MD: 0.04 mmol/L; 95%CI: -0.09, 0.28), but did find statistically significant differences in HDL-C (MD: -0.05 mmol/L; 95%CI: -0.07, -0.03).

VII. Blood pressure.

A . Systolic blood pressure (SBP) . Various studies found significantly lower mean levels of systolic blood pressure (SBP) levels in vegetarians compared to the general population [ 33 – 36 ]. Specifically, Gibbs et al. [ 33 ] reported a SMD of -5.47 mmHg (95%CI: -7.60, -3.34; p<0.00001) in ovo-lacto-vegetarians, as did Lee et al. [ 34 ] reporting a SMD of -1.75 mmHg (95%CI: -5.38, 1.88; p = 0.05); furthermore, they reported a SBP decreased by -2.66 mmHg (95%CI: -3.76, -1.55), in people adopting generic vegetarian diets. Moreover, Garbett et al. [ 35 ] reported a 33% lower prevalence of hypertension in vegetarians vs. nonvegetarians. On the contrary, Schwingshackl et al. [ 36 ], analyzing data from 67 clinical trials overall including 17,230 pre-hypertensive and hypertensive adult patients with a BMI between 23.6 and 45.4 kg/m 2 , followed for 3 to 48 months, did not find any significant reductions in SBP associated with vegetarian diet.

Four reviews investigated the differences in SBP between vegans and non-vegans. Benatar et al. and Lee et al. [ 25 , 34 ] reported significantly lower mean SBP levels in vegans vs. omnivores (MD: -2.56 mmHg; 95%CI: -4.66, -0.45; and WMD: -3.12 mmHg; 95%CI: -4.54, -1.70; p<0.001, respectively). On the other hand, Gibbs et al. [-1.30 mmHg (95%CI: -3.90,1.29)] and Lopez et al. (-1.33 mmHg; 95%CI: −3.50, 0.84; P = 0.230) [ 33 , 37 ] did not find any significant difference in mean SBP levels between vegans and omnivores.

Both reviews [ 32 , 38 ] focusing on SBP in mixed-plant-based dietary patterns found significantly lower levels in vegetarians than in omnivores. The meta-analysis by Picasso et al. [ 32 ], based on 4 RCTs did not find any differences, alas, analyzing 42 cross sectional studies, they described a MD of -4.18 mmHg (95%CI -5.57, -2.80; p<0.00001), in agreement with Yokoyama et al. [ 38 ], who reported a MD of -4.8 mmHg (95%CI: -6.6, -3.1; p<0.001; I 2 = 0) according to the 7 controlled trials, 6 of which being randomized (311 participants), included in the analysis, and of -6.9 mmHg (95%CI: -9.1, -4.7; p<0.001; I 2 = 91.4) based on the other 32 observational studies (21,604 participants).

B . Diastolic blood pressure (DBP) . Garbett et al. [ 35 ] reported reduced mean diastolic blood pressure (DBP) values in vegetarians vs. omnivores, confirmed by the analysis of Gibbs et al. [ 33 ] (WMD: –2.49 mmHg; 95%CI: –4.17, –0.80; p = 0.004; I 2 = 0%) in ovo-lacto-vegetarians, by Lee et al. [ 34 ] [WMD: -1.69 mmHg (95%CI: -2.97, -0.41; p<0.001)] who included 15 randomized controlled trials (N = 856) performed in vegetarians; and by Yokoyama et al. [ 38 ], who highlighted a MD -2.2 mmHg (95%CI: -3.5, -1.0; p<0.001; I 2 = 0%) and -4.7 mmHg (95%CI: -6.3, -3.1; p<0.001; I 2 = 92.6%) according to data from 7 controlled trials (N = 311) and 32 observational studies (N = 21,604), respectively. Conversely, Schwingshackl et al. [ 36 ] did not find significant differences between vegetarians and non-vegetarians.

Three reviews [ 25 , 34 , 37 ] examined the impact of vegan vs. non-vegan diet on DBP and described statistically significant reductions. Benatar et al. described reduction of DBP, corresponding to a MD of -1.33 mmHg (95%CI: -2.67, -0.02) [ 25 ]. Lee et al. described a reduction in DBP of a WMD of -1.92 mmHg (95%CI: -3.18, -0.66; p<0.001) [ 34 ]. Finally, Lopez et al. [ 37 ] described the same reduction amounting to WMD: -4.10 mmHg (95%CI: -8.14, -0.06).

Four studies agreed upon the lower mean DBP levels in subjects following mixed vegetarian diets as compared to omnivores [ 32 – 34 , 38 ], quantified as MD -3.03 mmHg (95%CI: -4.93, 1.13; p = 0.002) by Picasso et al. [ 32 ], and −2.2 mmHg (95%CI: −3.5, −1.0; p<0.001) and −4.7 mmHg (95%CI: −6.3, −3.1; p <0.001) by the analysis performed on clinical trials and observational studies, respectively, by Yokoyama et al. [ 38 ].

VIII. Body weight and body mass index (BMI).

Berkow et al. [ 39 ] identified 40 observational studies comparing weight status of vegetarians vs. non-vegetarians: 29 reported that weight/BMI of vegetarians of both genders, different ethnicities (i.e., African Americans, Nigerians, Caucasians and Asians), and from widely separated geographic areas, was significantly lower than that of non-vegetarians, while the other 11 did not find significant differences between the two groups. In female vegetarians, weight was 2.9 to 10.6 kg (6% to 17%) and BMI 2.7% to 15.0% lower than female non-vegetarians, while the weight of male vegetarians was 4.6 to 12.6 kg (8% to 17%) lower and the BMI 4.6% to 16.3% lower than that of male non-vegetarians. The review by Schürmann et al. [ 20 ], focusing on 8,969 children aged 0–18 years old found similar body weight in both vegetarian and vegan children as compared to omnivore ones. Dinu et al. [ 14 ] analyzed data from 71 studies (including 57,724 vegetarians and 199,230 omnivores) and identified a WMD BMI of -1.49 kg/m 2 (95%CI: -1,72, -1,25; p<0.0001) in vegetarians when compared to omnivores.

Barnard et al. [ 40 ] found a significant reduction in weight in pure ovolactovegetarians (−2.9 kg; 95% CI −4.1 to −1.6; P<0.0001), compared to non-vegetarians from control groups; furthermore, they found in vegans the mean effect was of -3.2 kg (95% CI: -4.0;-2.4, P: <0.0001); overall they included 490 subjects in their analysis, excluding subjects who did not complete the trials.

Benatar et al. [ 25 ]–including 12,619 vegans and 179,630 omnivores from 40 observation studies–and Dinu et al. [ 14 ]–based on 19 cross sectional studies, for a total of 8,376 vegans and 123,292 omnivores–reported the same exact result, with a mean lower BMI in vegans vs omnivores, equal to -1.72 kg/m 2 (95%CI: -2.30, -1.16) and -1.72 kg/m 2 (95%CI: -2.21,-1.22; p<0.0001), respectively. The meta-analysis by Long et al. [ 41 ], performed on 27 studies, reported a MD of -0.70 kg/m 2 (95%CI: -1.38, -0.01) for BMI in vegans vs. omnivores. A systematic review and meta-analysis by Agnoli et al. [ 42 ] found mean BMI to be lower in subjects adhering to mixed vegetarian diets as compared to omnivores. Additionally, Tran et al. [ 43 ] described weight reductions in clinically healthy patients, as well as in people who underwent vegetarian diets as a prescription, but no meta-analysis was performed.

Finally, Huang et al. [ 44 ] found significant differences in both vegans and vegetarians, who were found to have lost weight after having adopted the diet as a consequence of being assigned to the intervention group in their randomized studies. For vegetarians the WMD was -2.02 kg (95%CI: -2.80 to -1.23), when compared to mixed diets, and for vegans the WMD was -2.52 kg (95%CI: -3.02 to -1.98), when compared to vegetarians.

IX. Glucose metabolism.

Viguiliouk et al. [ 24 ] found a significant reduction in HbA1c (MD: −0.29%; 95%CI: −0.45, −0.12) and fasting glucose (MD: −0.56 mmol/L; 95%CI: −0.99, −0.13) in vegetarians vs. non-vegetarians.

The meta-analysis by Dinu et al. [ 14 ], reported for vegetarians (2256) vs omnivores (2192) WMD: -0.28 mmol/L (95%CI: -0.33, -0.23) in fasting blood glucose.

These findings were confirmed by Picasso et al. [ 32 ] who found a MD of -0.26 mmol/L (95% CI: -0.35, -0.17) in fasting glucose in mixed-vegetarian diets as compared to omnivores.

A meta-analysis by Long et al. [ 41 ], based of 27 cross sectional studies, showed a MD for homeostasis model assessment of insulin resistance -measured as HOMA-IR, a unitless measure ideally less than one- of -0.75 (95%CI: -1.08, -0.42), fasting plasma glucose in vegetarians who adhered also to an exercise intervention as compared to omnivores.

Lee & Park [ 45 ] reported a significantly lower diabetes risk (OR 0.73; 95%CI: 0.61, 0.87; p<0.001) in vegetarians vs. non-vegetarians, being the association stronger in studies conducted in the Western Pacific region and Europe/North America than in those from Southeast Asia.

Regarding vegans, the review by Benatar et al. [ 25 ] determined a mean reduction of 0.23 mmol/L (95%CI: -0.35, -0.10) of fasting blood glucose in vegans (N = 12,619) as compared to omnivores (N = 179,630). The finding was in line with Dinu et al. [ 14 ], who reported a WMD of -0.35 mmol/L (95%CI: -0.69, -0.02; p = 0.04) of fasting blood glucose in vegans (n = 83) than omnivores (n = 125).

A systematic review, finally, including 61 studies [ 42 ] found mean values of fasting plasma glucose, and T2D risk to be lower in subjects following mixed vegetarian diets as compared to omnivores.

X. Cardiovascular events.

Huang et al. [ 46 ] found a significantly lower risk of ischemic heart disease (IHD) (RR: 0.71; 95%CI: 0.56, 0.87), but no significant differences for cerebrovascular mortality between vegetarians and non-vegetarians. The review by Remde et al. [ 47 ] was not conclusive, as only a few studies showed a reduction of the risk of CVDs for vegetarians versus omnivores, while the others did not find any significant results.

Dybvik et al. [ 48 ] based on 13 cohort studies for a total of 844,175 participants (115,392 with CVDs, 30,377 with IHD and 14,419 with stroke) showed that the overall RR for vegetarians vs. nonvegetarians was 0.85 (95%CI: 0.79–0.92, I 2 = 68%; 8 studies) for CVD, 0.79 (95%CI: 0.71–0.88, I 2 = 67%; 8 studies) for IHD, 0.90 (95%CI: 0.77–1.05, I 2 = 61%; 12 studies) for total stroke, while the RR of IHD in vegans vs. omnivores was 0.82 (95%CI: 0.68–1.00, I 2 = 0%; 6 studies).

The meta-analysis by Kwok et al. [ 49 ], based on 8 studies including 183,321 subjects comparing vegetarians versus non-vegetarians. They identified a significant reduction of IHD in the Seventh Day Adventist (SDA) cohort, who primarily follow ovo-lacto-vegetarian diets, while other non-SDA vegetarian diets were associated only with a modest reduction of IHD risk, raising the concern that other lifestyle factors typical of SDA and, thus not generalizable to other groups, play a primary role on outcomes. IHD was significantly reduced in both genders (RR: 0.60; 95%CI: 0.43, 0.83), while the risk of death and cerebrovascular disease and cardiovascular mortality risk reduction was significantly reduced only in men. No significant differences were detected for the risk of cerebrovascular events.

The meta-analysis by Lu et al. [ 50 ] -657,433 participants from cohort studies- reported a lower incidence of total stroke among vegetarians vs. nonvegetarians (HR = 0.66; 95%CI = 0.45–0.95; I 2 = 54%), while no differences were identified for incident stroke.

The descriptive systematic review by Babalola et al. [ 3 ] reported that adherence to a plant-based diet was inversely related to heart failure risk and advantageous for the secondary prevention of CHD, particularly if started from adolescence. Another review by Agnoli et al. [ 42 ], confirmed a lower incidence of CVDs associated with mixed vegetarian diets as compared to omnivorous diets. Finally, Chhabra et al. [ 51 ] found that vegetarian diet, particularly if started in adolescence and associated with vitamin B intake, can reduce the risk of stroke.

Gan et al. [ 52 ] described a lower risk of CVDs (RR 0.84; 95% CI 0.79 to 0.89; p < 0.05) in high, vs. low, adherence plant based diets, but the same association was not confirmed for stroke (RR 0.87; 95% CI: 0.73, 1.03).

Group 2: Pregnancy outcomes

The meta-analysis by Foster et al. [ 53 ], performed on 6 observational studies, found significantly lower zinc levels in vegetarians than in meat eaters (-1.53 ± 0.44 mg/day; p = 0.001), but no association with pregnancy outcomes, specifically no increase in low children birth weight. The finding was confirmed by Tan et al. [ 54 ], who similarly reported no specific risks, but reported that Asian (India/Nepal) vegetarian mothers exhibited increased risks to deliver a baby with Low Birth Weight (RR: 1.33 [95%CI:1.01, 1.76, p =  0.04, I 2 = 0%]; nonetheless, the WMD of neonatal birth weight in five studies they analyzed suggested no difference between vegetarians and omnivores.

To our knowledge, no reviews/meta-analyses have assessed the risk of zinc deficiency and its association with functional outcomes in pregnancy in relation to mixed or vegan diets.

Group 3: Cancer

The meta-analysis by Parra-Soto et al. [ 55 ], based on 409,110 participants from the UK Biobank study (mean follow-up 10.6 years), found a lower risk of liver, pancreatic, lung, prostate, bladder, colorectal, melanoma, kidney, non-Hodgkin lymphoma and lymphatic cancer as well as overall cancer (HR ranging from 0.29 to 0.70) determined by non-adjusted models in vegetarians vs. omnivores; when adjusted for sociodemographic and lifestyle factors, multimorbidity and BMI, the associations remained statistically significant only for prostate cancer (HR 0.57; 95%CI: 0.43, 0.76), colorectal cancer (HR 0.73; 95%CI: 0.54, 0.99), and all cancers combined (HR 0.87; 95%CI 0.79, 0.96). When colorectal cancer was stratified according to subtypes, a lower risk was observed for colon (HR 0.69; 95%CI: 0.48, 0.99) and proximal colon (HR 0.43; 95%CI: 0.22, 0.82), but not for rectal or distal cancer.

Similarly, the analysis by Huang et al. [ 46 ], based on 7 studies for a total of 124,706 subjects, reported a significantly lower overall/total cancer incidence in vegetarians than non-vegetarians (RR 0.82; 95%CI: 0.67, 0.97).

Zhao et al. [ 56 ] found a lower risk of digestive system cancer in plant-based dieters (RR = 0.82, 95%CI: 0.78–0.86; p< 0.001) and in vegans (RR: 0.80; 95%CI: 0.74, 0.86; p<0.001) as compared to meat eaters.

Additionally, DeClercq et al. [ 57 ] reported a decreased risk of overall cancer and colorectal cancer, but inconsistent results for prostate cancer and breast cancer; this was substantiated by Godos et al. [ 58 ] found no significant differences in breast, colorectal, and prostate cancer risk between vegetarians and non-vegetarians.

The umbrella review by Gianfredi et al. [ 59 ], did describe a lower risk of pancreatic cancer associated with vegetarian diets.

Dinu et al. [ 14 ] reported a reduction in the risk of total cancer of 8% in vegetarians, and of 15% in vegans, as compared to omnivores. They described lower risk of cancer among vegetarians (RR 0.92; 95%CI 0.87, 0.98) and vegans (RR: 0.85; 95%CI: 0.75,0.95); nonetheless, they also described non-significant reduced risk of mortality from colorectal, breast, lung and prostate cancers. Regarding the latter, a meta-analysis by Gupta et al. [ 60 ] on prostate cancer risk found a decreased hazard ratio for the incidence of prostate cancer (HR: 0.69; 95%CI: 0.54–0.89, P<0.001) in vegetarians as compared to omnivores from the evidence coming from 3 studies. In the vegan population, similar results were observed from the only included study (HR: 0.65; 95%CI: 0.49–0.85; p<0.001).

Group 4: Death by cardiometabolic diseases and cancer

According to Huang et al. [ 46 ], the mortality from IHD (RR: 0.71; 95%CI: 0.56, 0.87), circulatory diseases (RR: 0.84; 95%CI: 0.54, 1.14) and cerebrovascular diseases (RR: 0.88; 95%CI: 0.70, 1.06) was significantly lower in vegetarians than in non-vegetarians.

The analysis by Dinu et al. [ 14 ] performed on 7 prospective studies, overall including 65,058 vegetarians, reported a 25% reduced mortality risk from ischemic heart diseases (RR 0.75; 95%CI: 0.68, 0.82; p<0.001), but no significant differences were found analyzing 5 cohort studies in terms of mortality from CVDs, cerebrovascular diseases, nor colorectal, breast, prostate, and lung cancer. Regarding vegans, they analyzed 6 cohort studies, and found no differences in all-cause mortality, but significant differences in cancer incidence (RR: 0.85; 95%CI: 0.75, 0.95), indicating a protective effect of vegan diets.

The literature search did not identify studies focusing on mortality risk for cardiometabolic and cancer diseases in vegans.

Quality of the included studies

The quality of the 48 reviews and meta-analyses included in this umbrella review was assessed through the AMSTAR-R tool. Results are reported in S1 Table . Overall, the average quality score was 28, corresponding to mean quality. However, 36 studies (75%) scored between 60% and 90% of the maximum obtainable score, and can, therefore, be considered of good/very good quality. The least satisfied item on the R-AMSTAR grid was #8 -scientific quality of included studies used to draw conclusions-, where as many as 19 studies (39.6%) failed to indicate the use of study-related quality analysis to make recommendations. This finding should be read in conjunction with the missing quality analysis in 15 studies (31.3%)–Item #7 scientific quality of included studies assessed and documented-. Item #10, regarding publication bias, was the second least met item, in which 18 studies (37.5%) did not perform any analysis on this type of bias. 16 studies (33.3%) lacked to indicate careful exclusion of duplicates (Item #2), but also the presence of conflict of interest (Item #11). This point is certainly another important piece to consider in the overall quality assessment of these articles. All these considerations give us a picture of a general low quality of the publications found, lowering the strength of evidence as well as the external validity of the results.

This umbrella review provides an update on the benefits associated with the adoption of A/AFPDs in reducing risk factors associated with the development of cardiometabolic diseases and cancer, considering both the adult and the pediatric population, as well as pregnant women.

Compared to omnivorous regimens, vegetarian and vegan diets appear to significantly improve the metabolic profile through the reduction of total and LDL cholesterol [ 14 – 21 , 23 , 25 ], fasting blood glucose and HbA1c [ 14 , 24 , 25 , 37 , 39 – 41 ], and are associated with lower body weight/BMI, as well as reduced levels of inflammation (evaluated by serum CRP levels [ 27 , 30 ]), while the effect on HDL cholesterol and triglycerides, systolic and diastolic blood pressure levels remains debated. A much more limited body of literature suggested vegetarian, but not vegan diets also reduce ApoB levels further improving the lipid profile [ 61 ].

It should be remarked that, in the majority of the cases, people adopting plant-based diets are more prone to engage in healthy lifestyles that include regular physical activity, reduction/avoidance of sugar-sweetened beverages, alcohol and tobacco, that, in association with previously mentioned modification of diet [ 62 ], lead to the reduction of the risk of ischemic heart disease and related mortality, and, to a lesser extent, of other CVDs.

The adoption of vegan diets is known to increase the risk of vitamin B-12 deficiency and consequent disorders–for which appropriate supplementation was recommended by a 2016 position paper of the Academy of Nutrition and Dietetics’ [ 5 ], but, apparently, does not modify the risk of pregnancy-induced hypertension nor gestational diabetes mellitus [ 53 , 54 ].

The three meta-analyses [ 46 , 55 , 57 ] that analyzed the overall risk of cancer incidence in any form concordantly showed a reduction in risk in vegetarians compared to omnivores. These general results were inconsistent in the stratified analyses for cancer types, which as expected involved smaller numbers of events and wider confidence intervals, especially for less prevalent types of cancers.

The stratified analyses in the different reviews did not show any significant difference for bladder, melanoma, kidney, lymphoma, liver, lung, or breast cancer. Conversely the three meta-analyses that addressed colorectal cancer [ 55 , 57 , 58 ] showed a decrease in risk in two out of three with one not showing a significant difference in vegetarians versus omnivores for the generic colorectal tract.

Interestingly, one review [ 55 ] showed how analysis with even more specific granularity could reveal significant differences in particular subsets of cancers, e.g., distal, and proximal colon. Also, another recent review found significant results for pancreatic cancer [ 59 ].

Our umbrella review seems consistent with other primary evidence that links the consumption of red processed meats to an increased risk of cancers of the gastro-intestinal tract [ 63 ]. The association certainly has two faces, because while a potential risk of cancer given by increased red meat consumption can be observed, the potential protective factor given by increased fruit and vegetable consumption, shown by other previous evidence, must also be considered [ 64 ].

It has also been described that vegetarians, in addition to reduced meat intake, ate less refined grains, added fats, sweets, snacks foods, and caloric beverages than did nonvegetarians and had increased consumption of a wide variety of plant foods [ 65 ]. Such a dietary pattern seems responsible for a reduction of hyperinsulinemia, one of the possible factors for colorectal cancer risk related to diet and food intake [ 66 , 67 ]. In the same manner, some research has suggested that insulin-like growth factors and its binding proteins may relate to cancer risk [ 68 , 69 ]. This dietary pattern should not be regarded as a universal principle, as varying tendencies have been observed among vegetarians and vegans in different studies. This pattern of consumption may potentially negate the anticipated beneficial effects of their diets.

Also, some protective patterns can be attributed to the effects of bioactive compounds of plant foods, these being primary sources of fiber, carotenoids, vitamins, minerals, and other compounds that have been associated with anti-cancer properties [ 70 , 71 ]. The protective patterns are likely attributed to the mechanistic actions of the many bioactives found in plant foods such as fiber, carotenoids, vitamins, and minerals with plausible anti-cancer properties. These ranged from epigenetic mechanisms [ 72 ], to immunoregulation, antioxidant and anti-inflammatory activity [ 73 , 74 ].

Finally, increased adiposity could be another pathway by which food intake is associated with these types of cancers. Since our umbrella review has demonstrated that vegetarian diets are associated with lower BMI, this might be another concurrent factor in the decreased risk for pancreatic and colorectal cancers in vegetarians.

Inflammatory biomarkers and adiposity play pivotal roles in the genesis of prostate cancer [ 75 , 76 ], hence the same etiological pathways might be hypothesized even for the increase of this type of cancer in people adopting an omnivorous diet.

The study presents several noteworthy strengths in its methodological approach and thematic focus. It has employed a rigorous and comprehensive search strategy involving two major databases, PubMed, and Scopus, spanning over two decades of research from 1 st January 2000 to 31 st June 2023, thereby ensuring a robust and exhaustive collection of pertinent literature. By utilizing an umbrella review, the research enables the synthesis of existing systematic reviews and meta-analyses, providing a higher level of evidence and summarizing a vast quantity of information. Furthermore, its alignment with current health concerns, specifically targeting cardiovascular diseases and cancer, makes the study highly relevant to ongoing public health challenges and positions it as a valuable resource for informing preventive measures and dietary guidelines. The deployment of blinded and independent assessments by multiple raters and investigators fortifies the research by minimizing bias and reinforcing the reliability of the selection, quality assessment, and data extraction processes. Quality assessment is standardized using the revised AMSTAR-R 11-item tool, and transparency is fostered through registration on PROSPERO, thus enhancing the credibility of the study. Lastly, the study’s detailed analysis and reporting, particularly the extraction of specific health measures such as cholesterol levels, glucose levels, blood pressure, and cancer risks, contribute to the comprehensiveness of the data synthesis, thereby underlining the overall integrity and significance of the research.

Main limitations to data analysis and interpretation are intrinsic to the original studies and consist in the wide heterogeneity in terms of sample size, demographic features, and geographical origin of included subjects, dietary patterns–not only in terms of quality, but, even more important and often neglected, quantity, distribution during the day, processing, cooking methods–and adherence, and other lifestyle confounders. In this regard, it is worth to mention that the impact of diet per se on the development of complex disorders (i.e. CVDs and cancer) and related mortality is extremely difficult to assess [ 71 ], especially in large populations, characterized by a highly heterogeneous lifestyle. It should also be considered the heterogeneity in dietary and lifestyle habits among countries, according to which the adoption of A/AFPDs could modify significantly habits in some countries, but not in others, and consequently have an extremely different impact on the risk of developing cardiometabolic disorders and cancer [ 25 ]. Furthermore, due to the nature of umbrella reviews, the present work may not include novel associations which were excluded from the analyzed reviews, as the main aim was to summarize secondary studies, such as reviews and meta-analyses. Finally, studies assessing the benefit of A/AFPDs on cancer risk are also limited by the heterogeneity in the timing of oncological evaluation and, therefore, disease progression, as well as in the histological subtypes and previous/concomitant treatments [ 72 – 75 ].

In conclusion, this umbrella review offers valuable insights on the estimated reduction of risk factors for cardiometabolic diseases and cancer, and the CVDs-associated mortality, offered by the adoption of plant-based diets through pleiotropic mechanisms. Through the improvement of glycolipid profile, reduction of body weight/BMI, blood pressure, and systemic inflammation, A/AFPDs significantly reduce the risk of ischemic heart disease, gastrointestinal and prostate cancer, as well as related mortality.

However, data should be taken with caution because of the important methodological limitation associated with the original studies. Moreover, potential risks associated with insufficient intake of vitamin and other elements due to unbalanced and/or extremely restricted dietary regimens, together with specific patient needs should be considered, while promoting research on new and more specific markers (i.e. biochemical, genetic, epigenetic markers; microbiota profile) recently associated with cardiometabolic and cancer risk, before suggesting A/AFPDs on large scale.

Supporting information

S1 table. r-amstar..

https://doi.org/10.1371/journal.pone.0300711.s001

S2 Table. PRISMA 2020 checklist.

https://doi.org/10.1371/journal.pone.0300711.s002

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