research studies on vegetarianism

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• Published: 22 April 2020

Prevalence and psychopathology of vegetarians and vegans – Results from a representative survey in Germany

• Georgios Paslakis 1 , 2 ,
• Candice Richardson 1 ,
• Mariel Nöhre 3 ,
• Elmar Brähler 4 , 6 ,
• Christina Holzapfel 5 ,
• Anja Hilbert 6 &
• Martina de Zwaan 3  

Scientific Reports volume  10 , Article number:  6840 ( 2020 ) Cite this article

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An Author Correction to this article was published on 10 November 2020

This article has been updated

The aim of the study was to investigate the prevalence of, and attitudes toward, vegetarianism and veganism. We also assessed the association between vegetarianism/veganism and eating disorder, depressive, and somatic symptoms. A cross-sectional questionnaire survey in adults in Germany that was representative in terms of age, gender, and educational level was carried out. Data from 2449 adults (53.5% females) were included. Mean age was 49.6 (SD 17.1) years. A total of 5.4% of participants reported following a vegetarian or vegan diet. While the majority of participants agreed that vegetarian diets are healthy and harmless (56.1%), only 34.8% believed this to be true of vegan diets. The majority of participants also believed that a vegetarian (58.7%) or vegan (74.7%) diet can lead to nutritional deficiency. Female gender, younger age, higher education, lower body mass index (BMI), and higher depressive and eating disorder symptoms were found to be associated with vegetarianism/veganism. We did not find increased physical complaints in the group of vegetarians/vegans. Our results point toward a moderate prevalence of vegetarianism/veganism among the general population. Our findings suggest that health care professionals should keep eating disorder pathology, affective status in mind when dealing with individuals who choose a vegetarian/vegan dietary pattern.

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Introduction.

To date research about vegetarianism and veganism is still young even though plant-based nutrition seems to have gained increasing popularity and represents a growing social movement 1 . Vegetarianism is a generic term that encompasses a variety of dietary patterns that each involves, to some extent, the avoidance of meat 2 . While omnivores consume all types of animal products 3 , true vegetarians are defined as those who do not eat any meat, poultry, or fish 4 . Vegetarians may be further sub-classified based on the inclusion of eggs (ovo-vegetarians), diary (lacto-vegetarians), fish (pesco-vegetarians), poultry (pollo-vegetarians), or a combination of these foods in their diet 2 , 5 , 6 . Finally, vegans are those who refrain from eating any animal products, including meat, fish, dairy, eggs, and other animal-derived foods 3 . Individuals may adopt a vegetarian diet for a variety of reasons which may be ethical, moral, religious, environmental, health-related, or concerns about animal welfare 7 . The majority of recent studies suggest that ethical concerns are the most common motivation for adopting a vegetarian diet, followed by health considerations 3 , 5 , 8 . While health vegetarians avoid meat in order to derive the perceived health benefits of a vegetarian diet or to lose weight, ethical vegetarians avoid meat for animal welfare reasons 9 . The aim of the present study was to investigate the prevalence of, and attitudes toward, vegetarianism and veganism in a representative sample of the general adult population in Germany.

The prevalence of vegetarianism varies around the world with recent polls indicating that approximately 5% of Americans 10 , 8% of Canadians 11 , and 4.3% of Germans 6 follow a vegetarian diet. However, the highest proportion of vegetarians are found in India, where they comprise 30% of the population 12 , 13 . Veganism is less common with the prevalence reported to be about 2% in the United States 10 and less than 1% in Germany 14 . In several studies, education and income were found to be inversely associated with meat consumption 14 , 15 , 16 . Subsequent research conducted within Central European countries also indicates that vegetarians tend to be more educated and affluent than omnivores 14 , 17 . Allès et al . 18 confirmed that vegetarians tend to be more educated than omnivores, but also found out that vegans tend to have lower educational attainment. Additionally, women are far more likely to be vegetarian than men 8 ; even among non-vegetarians, women have been found to eat considerably less meat than men 1 , 14 , 19 , 20 .

Although strict and unbalanced dietary restrictions can pose a risk of micronutrient deficiencies 2 , it is the position of the Academy of Nutrition and Dietetics that appropriately planned vegetarian diets are nutritionally adequate and may be beneficial for health 21 . A comprehensive meta-analysis of 80 studies provides evidence for the link between a vegetarian diet and a lowered risk of cardiovascular disease, type 2 diabetes, obesity, and certain types of cancer 22 . Vegetarianism has also been associated with reduced risk of hypertension, diverticular disease, degenerative arthritis, and metabolic syndrome in other studies 4 , 23 . Also, the use of vegetarian and vegan diets is often associated with other health behaviors including non-smoking and regular physical activity 1 . Additionally, studies conducted in Western countries have consistently shown that vegetarians have a lower BMI compared to their non-vegetarian counterparts, with vegans having the lowest BMI 24 , 25 , 26 .

There is mixed evidence as to whether vegetarianism is associated with more positive or negative mental health 27 . Although vegetarians have reported more positive mood in some studies 28 , 29 , they have described more psychological symptoms associated with anxiety and depression in others 30 , 31 . Similarly, while some studies 32 , 33 , 34 have found a higher risk of depression among vegetarians, others 5 , 28 show no significant difference between vegetarians and omnivores. Furthermore, adolescent vegetarians were more likely to be depressed 35 and have contemplated suicide 36 when compared to adolescent omnivores. Adherence to a vegetarian diet has been hypothesized to be a factor in the development and maintenance of disordered eating 5 as the restrictive nature of the diet may be used as a socially acceptable way to refrain from eating specific foods 3 . The majority of studies 36 , 37 , 38 , 39 suggest that vegetarians exhibit greater levels of disordered eating than omnivores; however, two recent studies suggest that this may not always be the case 40 , 41 . Indeed, in one study by Timko et al . 5 , semi-vegetarians, defined as those who exclude red meat from their diet, were found to have the highest level of eating pathology, while true vegetarians and vegans appeared healthiest in regards to eating and body weight. Thus, it is important to understand attitudes toward plant-based diets and the potential association with eating disorder, depressive, and somatic symptoms, as these findings, in conjunction with those from additional longitudinal studies, can lead to the development of more specific guidelines for healthcare professionals to monitor patients that follow these types of diets.

While the primary aim of this study was to investigate the prevalence of, and attitudes toward, vegetarianism and veganism, we also assessed the association between vegetarianism/veganism and eating disorder symptoms, depressive symptoms, and the presence of somatic symptoms. We expected that consistent with previous studies, vegetarians/vegans would display a higher burden of eating disorder and general psychopathology.

Recruitment

A random sample of German residents aged 14 years and older (age range 14 to 91 years) were recruited as part of a cross-sectional survey on physical and mental well-being. For the purposes of the present investigation we only assessed adults (≥18 years of age). A demographic consulting company (USUMA GmbH, Berlin, Germany) assisted with sampling and data collection. The procedure was designed to yield a nation-wide sample representative in terms of age, gender, and educational level over the fieldwork period from May to July 2018. Sociodemographic data were collected in-person by trained interviewers and participants also completed a battery of self-report questionnaires.

Data acquisition

In Germany, no directory is generally available that contains the addresses of all private households or individuals, which could be used by market research agencies as a sampling frame. The data collected by the local authorities are only available for surveys considered to be of major public interest. A group of agencies called the “Arbeitsgemeinschaft ADM-Stichproben” closes this gap by providing a sampling frame to member agencies, the so-called “ADM-Sampling-System for Face-to-Face Surveys”. This frame allows representative face-to-face samples to be drawn for all households in Germany and for all people living in those households. In addition, the main statistical data are provided on a detailed level for this population. The ADM-Sampling-System is described in detail elsewhere 42 , 43 .

The participation rate was 46.9% (2531 of 5393 persons), taking into account all refusals to participate, as well as interviews that failed to take place due to respondents’ illness or being otherwise unavailable during the fieldwork. All participants provided their written informed consent in accordance with the Helsinki declaration. The study was approved by the Ethics Committee of the Medical School of the University of Leipzig.

The following sociodemographic data were assessed: gender (male and female), age (distinguished according to groups: 18–24, 25–34, 35–44, 45–54, 55–65, >65 years), educational level (<12 and ≥12 years), monthly income (0 to <1000, 1000–2500, and ≥2500 euros per month), population size (<5000, 5000–50000, and ≥50000 residents). The BMI was calculated based on participants’ self-reported height and weight.

Dietary assessment

To assess self-reported dietary patterns, participants were asked the following question “Have you been consciously eating a vegetarian diet for at least 2 weeks?” This question has been repeated for vegan diet. It was explained to participants that vegetarian means omitting meat, but eating plants and milk products, and vegan means omitting all foods of animal origin.

Subsequently, participants were presented with a series of 11 statements about vegetarian diets. The same statements were asked for a vegan diet. Participants responded to each statement using a 4-point Likert scale ranging from “totally agree” to “totally disagree”. All statements were short and simple:

A vegetarian diet is completely healthy and harmless.

A vegetarian diet can lead to a nutritional deficiency.

People who follow a vegetarian diet are seldom overweight.

Individuals who follow a vegetarian diet are more productive.

A vegetarian diet is able to prevent disease.

A vegetarian diet is good for the environment.

A vegetarian diet is less cruel to animals.

People who follow a vegetarian diet are made fun of.

A vegetarian diet is not tasty.

A vegetarian diet is expensive.

People who eat a vegetarian diet do so out of ethical motivation.

Additionally, omnivores were asked if a vegetarian or vegan diet would be a viable diet for them to pursue. All questions and statements were constructed and finally chosen from a larger pool by experienced nutritionists, physicians and psychologists.

Psychological assessment

Participants also completed the Patient Health Questionnaire-4 (PHQ-4) 44 , the Eating Disorder Examination-Questionnaire 8 (EDE-Q8) 45 , and a brief form of the Giessen Subjective Complaints List (GBB-8) 46 . The PHQ-4 allows for the brief measurement of depression and anxiety based on participants’ responses to 4 items on a Likert scale ranging from “not at all” to “nearly every day”. Total scores range from 0 to 12, and correspond to no (0–2), mild (3–5), moderate (6–8), or severe (9–12) psychological distress 44 . The EDE-Q8 is an 8-item self-report questionnaire used to assess eating disorder psychopathology. Scores range from 0 to 6, with higher scores indicating greater psychopathology 45 . Similarly, the GBB-8 is a brief, self-report questionnaire used to assess somatic symptom strain. Total scores range from 0 to 32, while scores on the four subscales (exhaustion, gastrointestinal complaints, musculoskeletal complaints, and cardiovascular complaints) range from 0 to 8 with higher scores indicating greater symptom strain 46 .

Statistical analyses

For analysis of the dietary statements, the answers “totally agree” and “agree” were grouped together, as were “disagree” and “totally disagree”. T-Tests or Chi-square tests were performed appropriately when comparing vegetarians/vegans with omnivores. In order to examine the predictive value of the independent variables, a binary logistic regression was performed with vegetarianism and veganism as dependent variable. The level of significance was set at p ≤ 0.05. Bonferroni correction for multiple testing was performed according to the number of independent variables in each hypothesis testing. Unweighted data were used. Statistical analyses were performed using SPSS (IBM SPSS Statistics for Windows, Version 25.0. Armonk, NY: IBM Corp.).

Participants

A total of 2531 individuals participated in the survey. Of those, 82 were excluded for being younger than 18 years. Thus, data from a total of 2449 adults were analyzed. This cohort consisted of 46.5% (1138/2449) males and 53.5% (1311/2449) females. Mean age was 49.6 (SD 17.1) years, and 40.9% (1001/2449) of participants were aged older than 55 years. Additionally, the mean BMI was 25.9 (SD 2.1) kg/m 2 . More details on socio-demographics of the cohort are shown in Table  1 .

Prevalence of self-defined vegetarianism and veganism

When participants were asked whether they have followed a conscious vegetarian diet for at least two weeks, 5.2% (126/2444) indicated yes. The non-vegetarian participants were further asked whether a vegetarian diet would be a viable diet form to pursue. Of the 2316 respondents to this question, 11.2% (259/2316) indicated yes. In a similar manner, 1.3% (31/2446) of participants reported following a strict vegan diet. The non-vegan participants were further asked whether a vegan diet would be a potential diet form to adopt, to which 5.9% (142/2414) indicated yes.

There was considerable overlap in the endorsement of vegetarian and vegan dietary patterns. Of the 133 (5.4%) participants who reported following a vegetarian and/or vegan diet, 18% (24/133) answered “yes” to both questions, 76.7% (102/133) reported following a vegetarian but not a vegan diet, and 5.3% (7/133) indicated they followed a vegan but not vegetarian diet. Given this overlap, for the present analysis, those who endorsed a vegetarian and/or vegan diet were grouped together. Thus, the prevalence of current self-defined vegetarians/vegans was 5.4% in the present sample.

Attitudes toward vegetarian and vegan diets

When participants were asked about their attitudes toward a vegetarian diet, the majority of both vegetarians/vegans and omnivores agreed that a vegetarian diet is completely healthy and harmless, good for the environment, and less cruel to animals. The majority of both groups also believed that those who eat a vegetarian diet do so out of ethical motivation, and are seldom overweight. Conversely, the majority of both groups disagreed with the notions that vegetarians are made fun of and that a vegetarian diet is not tasty. While the majority of vegetarians/vegans agreed that vegetarians are more productive and that the diet can prevent disease, only a minority of omnivores agreed with these statements. Similarly, while the majority of omnivores agreed that a vegetarian diet is expensive and can lead to nutritional deficiencies, the majority of vegetarians/vegans disagreed with these statements. Full details are displayed in Table  2 .

Similarly, when asked about their attitudes toward a vegan diet, the majority of vegetarians/vegans and omnivores, again, agreed that those who eat a vegan diet do so out of ethical motivation, are seldom overweight, and that a vegan diet is good for the environment and less cruel toward animals. However, in opposition to their attitudes toward vegetarian diets, the majority of both groups believed that a vegan diet can lead to nutritional deficiency, and that those who follow a vegan diet are made fun of. While the majority of vegetarians/vegans agreed that a vegan diet is completely healthy and harmless, can prevent disease, and that those who follow a vegan diet are more productive, the majority of omnivores disagreed with these statements. Similarly, while the majority of omnivores agreed that a vegan diet is expensive and not tasty, the majority of vegetarians/vegans disagreed with these notions. Full details are displayed in Table  3 .

Comparison between self-defined vegetarians/vegans and omnivores

Comparing vegetarians/vegans to omnivores, no differences in income distribution or population size of the community or city of origin were found. Among vegetarians/vegans, a significantly higher proportion were female (73.7% vs. 26.3%; X 2 (1) = 23.174, p < 0.001). Additionally, vegetarians/vegans were significantly younger than omnivores (M = 40.9, SD = 15.5 vs. M = 50.0, SD = 17.0; t(2442) = −6.033, p < 0.001). Finally, 51.5% of vegetarians/vegans attained 12 or more years of education compared to 21.8% of omnivores (X 2 (1) = 61.531, p < 0.001). Vegetarians/vegans also had a significantly lower BMI compared to omnivores (M = 24.0, SD = 4.7 vs. M = 26.0, SD = 5.0; t(2423) = −4.555, p < 0.001). Similarly, vegetarians/vegans had significantly higher eating disorder psychopathology in the EDE-Q8 (M = 1.3, SD = 1.4 vs. M = 1.0, SD = 1.3; t(2440) = 2.619, p = 0.009), as well as slightly, but not significantly, higher depression scores in the PHQ-4 (M = 2.0, SD = 2.3 vs. M = 1.5, SD = 2.1; t(140) = 2.327, p = 0.21) scores compared to omnivores. More details are shown in Table  4 . In terms of somatic complaints, vegetarians/vegans and omnivores did not significantly differ in their experiences of exhaustion, gastrointestinal complaints, musculoskeletal complaints, cardiovascular complaints, or overall symptom strain (Table  5 ).

A binary logistic regression analysis was conducted to predict vegetarianism/veganism based on gender, age, education, population size, income, BMI, EDE-Q8 score, and PHQ-4 score. A significant regression model was found, χ 2 (8) = 835.0, p < 0.001: gender (female), (younger) age, (higher) education, (lower) BMI, (higher) PHQ-4 score, and (higher) EDE-Q8 score were significant statistical predictors of vegetarianism/veganism (Table  6 ).

The prevalence rate of self-defined vegetarians/vegans among the general German population found in the present investigation (n = 133, 5.4%) is comparable to that reported in an earlier German representative sample, in which the prevalence was found to be between 3% and 6% 14 . The current prevalence rate is also similar to those reported in US investigations 10 . A significant minority of omnivores reported that they would consider a vegetarian (11.2%) or vegan (5.9%) diet for themselves in the future showing that some people have an interest in adopting this kind of nutrition (“prospective vegetarianism”) 20 . Omnivores were more open to becoming vegetarian than to becoming vegan. However, meat consumption is still part of the traditional and social norm in Western societies 47 .

Regarding general attitudes toward vegetarian/vegan forms of diet in the general population, we noticed that both diet forms were considered expensive. Vegetarian and vegan diets are often perceived to be expensive 48 , and have therefore been associated with lower openness to try a vegetarian diet 49 . However, when compared to meat eaters, “true” vegetarians have been shown to report lower food expenditures 50 . While a vegetarian diet was considered to be healthy by most respondents, the majority did not think the same about vegan diets. This is in line with the German Nutrition Society which clearly states that a vegan diet cannot fulfill the daily recommendation for vitamin B12 intake and that supplementation is needed in most of the persons sticking on a vegan diet. Moreover, veganism is not recommended for pregnant and lactating women 51 . Additionally, almost two-third of the respondents said that vegans are made fun of and also a slight majority of respondents agreed that vegetarians are made fun of. Most respondents stated that vegetarian/vegan diet is less often associated with overweight. Vegan diet is not considered tasty. People have more negative beliefs about veganism than vegetarianism which is in line with literature. Literature also shows that vegetarians themselves report unfavorable social experiences 52 and biases with omnivores belittling their character 20 .

We found that female gender, younger age, lower BMI, higher depression scores, and higher eating disorder-related psychopathology were significantly associated with vegetarian/vegan diets. In terms of gender differences, this is entirely in accordance with the existing literature 1 , 8 , 14 . There is an extensive literature on the association between meat and masculinity 19 showing that men view meat as a more essential part of a proper diet. Thus it is not surprising that we found a higher proportion of females to be vegetarians/vegans. Similarly, we found that vegetarians/vegans were significantly younger than omnivores, as previously documented in multiple studies conducted among adults in Germany 14 , the UK, Canada, and the U.S 18 , 24 , 53 , 54 , 55 . Our findings are also in congruence with previous research showing an association between higher education and reduced meat consumption 14 , 15 , 16 , as over half of the vegetarians/vegans in our study attained 12 or more years of education compared to 22% of omnivores. Conversely, while previous research has documented greater affluence among vegetarians 14 , 17 , we found no difference in income distribution between vegetarians/vegans and omnivores in our sample. We also found vegetarians/vegans to have a lower BMI compared to their omnivorous counterparts; which is consistent with existing literature 10 , 24 , 25 , 26 .

Limited data is available on the associations between vegetarian diet and mental health 34 . While some studies have shown no significant differences in depressive symptoms between vegetarians and omnivores 5 , 28 , our results more closely align with those that have documented higher risk for 32 , 33 , 34 and more psychological symptoms associated with depression 30 , 31 among vegetarians/vegans. The prevalence of participants who screened positive for potential cases of depression and anxiety (PHQ-4 > 6) was 5.3% in omnivores and 8.5% in vegetarians/vegans. However, we cannot make any assumptions about causality. Do more depressed individuals select to follow a vegetarian/vegan diet or does following a vegetarian/vegan diet increase the risk for developing depression? It cannot be excluded that nutritional status may affect brain processes and may influence onset and maintenance of mental disorders 34 .

Our results allude to an association between choosing to subsist upon a diet excluding meat and displaying symptoms of disordered eating. The difference in EDE-Q8 scores remained even after adjusting for gender and age which are known to influence eating disorder symptoms. This result is in accordance to the majority of previous similar studies 36 , 37 , 38 , 39 , even though the overall scores in the present sample were close to scores found in the general German population 45 . In terms of the potential link between vegetarianism and the development of eating disorders, evidence from three retrospective chart reviews 56 , 57 , 58 show that approximately half of all patients diagnosed with anorexia nervosa report adhering to a vegetarian diet. Others have emphasized that this might represent a more orthorexic behavior with a fixation on health-conscious eating 59 . Furthermore, two-thirds of individuals with history of an eating disorder reported that their vegetarianism was related to the eating disorder as it allowed them to restrict caloric intake and increase feelings of control; however, the majority of these individuals also indicated that they adopted a vegetarian diet after the onset of their eating disorder 60 . Thus, vegetarianism may be a symptom of the disorder or a maintaining factor, rather than linked to its causal development 3 . As far as the clinical implications of our findings are concerned, our findings imply that health care professionals should keep the association between eating disorder psychopathology and vegetarian/vegan forms of diet in mind when dealing with individuals who choose this form of diet; especially in younger women. Similarly, affective status should be considered in the same group in question.

We did not find differences with regard to physical complaints between the groups of vegetarians/vegans and omnivores. Thus, although self-reported symptoms cannot be accounted for factual differences in health status between the two groups under investigation, we conclude that vegetarians did not differ in complaints of (somatoform) symptoms compared to the general omnivore population. In one German study vegetarians reported a better current health status than omnivores 14 . This finding is in contrast to another previous German investigation showing an increased prevalence for somatoform disorders in vegetarians 34 . Michalak et al . 34 found evidence for elevated prevalence rates in vegetarians not only for somatoform syndromes but also for depressive disorders, anxiety disorders as well as for eating disorders. This is the only study that did not rely on self-report but used clinical diagnoses of mental disorders as assessed with standardized diagnostic interviews and that controlled for socio-demographic characteristics. For depressive, anxiety and somatoform disorders the adoption of a vegetarian diet followed the onset of mental disorders and the authors hypothesized that a mental disorder increases the likelihood of choosing a vegetarian diet probably with the goal to positively influence the course of the disease.

There are some limitations to consider. The response rate was relatively low (46.9%), which is, however, common in general population research. The current use of vegetarian and vegan diets was self-reported, and it is known from previous studies that self-identified vegetarians do not necessarily completely abstain from meat 6 , 19 . Furthermore, we define “vegetarian/vegan” as a person who sticks to that diet for at least two weeks, which means, that this definition is rather lenient. Therefore, also short-term vegetarians/vegans might be within the survey. We did not assess the motivation for following a vegetarian or vegan diet. A further limitation lies in the lack of assessment of objective measures (e.g., BMI) and the reliance on self-reports. Additionally, considering that this was a cross-sectional study, and that the vegetarian/vegan group was mostly young females, it may be that young females are more prone to having an eating disorder regardless of the diet they follow. Thus, vegetarianism/veganism may be a symptom or maintaining factor of the disorder rather than linked to its causal development. Due to the cross-sectional design in this study, no conclusions can be made regarding the causality of the association between diet and the examined individual differences. In contrast, the strengths of our study are the inclusion of a large representative sample of the German population and the use of standardized questionnaires to assess depressive, eating disorder, and somatic symptoms.

Taken together, the prevalence of current and self-defined vegetarianism and veganism in the present research was 5.4% which is comparable to other German and international studies. People’s attitudes toward vegetarians and vegans still point toward some biases. Finally, the present survey showed that there are not only differences between self-defined vegetarians and omnivores in socio-demographics, but also in levels of eating-related symptoms and potential cases of depression and anxiety.

Data availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Change history

10 november 2020.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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G.P. and M.d.Z. designed the study. G.P. and C.R. conducted the statistical analyses. M.N., E.B., C.H., and A.H. participated in instrument selection and development of the questions on veganism and vegetarianism. The first draft was written by C.R. All authors reviewed the manuscript and accepted the final version.

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Paslakis, G., Richardson, C., Nöhre, M. et al. Prevalence and psychopathology of vegetarians and vegans – Results from a representative survey in Germany. Sci Rep 10 , 6840 (2020). https://doi.org/10.1038/s41598-020-63910-y

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The long-term health of vegetarians and vegans

Affiliation.

• 1 Cancer Epidemiology Unit, Nuffield Department of Population Health,University of Oxford,Richard Doll Building,Old Road Campus,Roosevelt Drive,Oxford OX3 7LF,UK.
• PMID: 26707634
• DOI: 10.1017/S0029665115004334

Vegetarians, who do not eat any meat, poultry or fish, constitute a significant minority of the world's population. Lacto-ovo-vegetarians consume dairy products and/or eggs, whereas vegans do not eat any foods derived wholly or partly from animals. Concerns over the health, environmental and economic consequences of a diet rich in meat and other animal products have focussed attention on those who exclude some or all of these foods from their diet. There has been extensive research into the nutritional adequacy of vegetarian diets, but less is known about the long-term health of vegetarians and vegans. We summarise the main findings from large cross-sectional and prospective cohort studies in western countries with a high proportion of vegetarian participants. Vegetarians have a lower prevalence of overweight and obesity and a lower risk of IHD compared with non-vegetarians from a similar background, whereas the data are equivocal for stroke. For cancer, there is some evidence that the risk for all cancer sites combined is slightly lower in vegetarians than in non-vegetarians, but findings for individual cancer sites are inconclusive. Vegetarians have also been found to have lower risks for diabetes, diverticular disease and eye cataract. Overall mortality is similar for vegetarians and comparable non-vegetarians, but vegetarian groups compare favourably with the general population. The long-term health of vegetarians appears to be generally good, and for some diseases and medical conditions it may be better than that of comparable omnivores. Much more research is needed, particularly on the long-term health of vegans.

Keywords: AHS-2 Adventist Health Study-2; EPIC-Oxford; European Prospective Investigation into Cancer and Nutrition-Oxford; Morbidity; Mortality; Vegan; Vegetarian.

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• Research Support, Non-U.S. Gov't
• Body Mass Index
• Cardiovascular Diseases / epidemiology
• Cardiovascular Diseases / prevention & control
• Diabetes Mellitus, Type 2 / epidemiology
• Diabetes Mellitus, Type 2 / prevention & control
• Diet, Vegan*
• Diet, Vegetarian*
• Health Status*
• Neoplasms / epidemiology
• Neoplasms / prevention & control
• Obesity / epidemiology
• Obesity / prevention & control
• Risk Factors
• Weight Gain

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• 16491/CRUK_/Cancer Research UK/United Kingdom
• MR/M012190/1/MRC_/Medical Research Council/United Kingdom

• Brief Report
• Open access
• Published: 23 November 2023

Vegetarian diets and risk of all-cause mortality in a population-based prospective study in the United States

• Keeley Blackie 1 ,
• Gerd Bobe 2 &
• Yumie Takata 3  

Journal of Health, Population and Nutrition volume  42 , Article number:  130 ( 2023 ) Cite this article

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The popularity of vegetarian diets has increased the need for studies on long-term health outcomes. A limited number of studies, including only one study from a non-vegetarian population, investigated the risk of mortality with self-identified vegetarianism and reported inconsistent results. This study evaluated prospective associations between vegetarian diets and all-cause mortality among 117,673 participants from the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial cohort study. Vegetarian diet status was self-identified on the questionnaire. Deaths were ascertained from follow-up questionnaires and the National Death Index database. Multivariable Cox regression models were used to estimate the risk of all-cause mortality in hazard ratio (HR) and 95% confidence intervals (CI). By diet group, there were 116,894 omnivores (whose diet does not exclude animal products), 329 lacto- and/or ovo-vegetarians (whose diet excludes meat, but includes dairy and/or eggs), 310 pesco-vegetarians (whose diet excludes meat except for fish and seafood) and 140 vegans (whose diet excludes all animal products). After an average follow-up of 18 years, 39,763 participants were deceased. The risk of all-cause mortality did not statistically significantly differ among the four diet groups. Comparing with the omnivore group, the HR (95% CI) were 0.81 (0.64–1.03) for pesco-vegetarian group, 0.99 (0.80–1.22) for lacto- and/or ovo-vegetarian group and 1.27 (0.99–1.63) for vegan group, respectively. Similarly, mortality risk did not differ when comparing lacto- and/or ovo-vegetarians plus vegans with meat/fish eaters (omnivores and pesco-vegetarians) (HR [95% CI] = 1.09 [0.93–1.28]). As this study is one of the two studies of vegetarianism and mortality in non-vegetarian populations, further investigation is warranted.

Introduction

Chronic diseases including cardiovascular disease (CVD), cancer, and diabetes are the leading cause of deaths in the US [ 1 ]. Between 1990 and 2010, unhealthful diets accounted for 26% and 22% of all-cause and CVD deaths, respectively [ 2 ]. Vegetarian diets have gained popularity due to potential health, environmental and sustainability benefits [ 3 ].

Several foods of plant origin have been associated with a lower risk of chronic diseases and their risk factors such as insulin resistance and high total blood cholesterol [ 3 , 4 , 5 , 6 , 7 ]. These beneficial effects are linked to being often less energy-dense and more nutrient-rich with higher amounts of fiber, vitamins, minerals and phytochemicals and lower amounts of total and saturated fats compared with animal products [ 3 ]. Despite these health benefits, specific micronutrient deficiencies are of concern for vegans because animal products are the only natural source of vitamin B 12 and provide more bioavailable iron and calcium [ 3 ].

Most previous observational studies and clinical trials lend support for protective effects of overall vegetarian diets or their specific components on risk of chronic diseases or their risk factors [ 5 , 6 , 7 ]. Few observational studies have investigated associations between vegetarian diets and all-cause mortality, and reported inconsistent associations [ 8 , 9 , 10 , 11 , 12 ]. Only one study was conducted in a general, non-vegetarian population in Australia and reported null association [ 11 ]. Hence, this study prospectively investigated whether self-identified vegetarian or vegan diets (i.e., lacto- and/or ovo-vegetarian, pesco-vegetarian, and vegan) compared with an omnivorous diet are associated with mortality risk in the US Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial cohort.

Study population

This study was based on data from the PLCO Cancer Screening Trial which originally aimed to assess effectiveness of early cancer detection and to investigate etiological factors of cancer. Between 1993 and 2001, 154,952 participants (age range: 55 to 74) were enrolled and randomized into the control (standard cancer screening method) or intervention (new method) arm [ 13 ]. At the time of randomization, participants filled out questionnaires on possible risk factors for cancer including demographics, smoking history, medical history, body weight and height, and dietary intakes. Starting in 1998, a new food frequency questionnaire, Diet History Questionnaire (DHQ) [ 14 ], was administered within five years of randomization. This study focused on 118,779 participants who completed the DHQ. After excluding missing or unclear responses to questions on vegetarianism, 117,673 participants were included in the analysis. All participants included in this study provided written, informed consent for all trial activities and future etiological research studies. The PLCO study was approved by the Institutional Review Boards (IRB) at National Cancer Institute. The IRB review at Oregon State University was exempt.

Dietary assessment and mortality ascertainment

The validated DHQ was self-administered and inquired about vegetarianism and habitual food and beverage intakes in the past 12 months [ 14 ]. Our analysis was based on questions about following any type of vegetarian diets and what foods they exclude from their diet entirely: meat (e.g., beef, pork, and lamb); poultry (e.g., chicken, turkey, and duck); fish and seafood; eggs; and dairy products (e.g., milk and cheese). The participants were classified into: (1) vegan (entirely excluding meat, poultry, fish and seafood, eggs and dairy products); (2) lacto- and/or ovo-vegetarian (entirely excluding meat, poultry, fish and seafood, but consuming dairy products and/or eggs); (3) pesco-vegetarian (entirely excluding meat, poultry, eggs and dairy products but consuming fish and seafood); and (4) omnivore (no exclusion of animal products). Deaths of participants were ascertained by annual study update questionnaires and regular linkage to the National Death Index database through 2018.

Statistical analysis

Baseline characteristics were compared among the four diet groups using analysis of variance for continuous variables and χ 2 -test for categorical variables. For risk of mortality, we used the Cox regression and modeled on the time from the date of DHQ completion to the first of the following: date of death, loss to follow-up, or December 31, 2018. The hazard ratio (HR) and corresponding 95% confidence intervals (CI) were calculated first for pesco-vegetarian, lacto- and/or ovo-vegetarian or vegan diet group using the omnivore group as reference and second for vegetarians (i.e., lacto-and/or ovo-vegetarians and vegans) using non-vegetarians (i.e., pesco-vegetarians and omnivores [meat/fish eaters]) as reference. The following variables were a priori selected based on previous studies [ 8 , 11 , 15 ]: age, sex, study center location and trial arm (as part of the original PLCO trial) in the minimally-adjusted model. The fully-adjusted model also included smoking status, pack-years of smoking, alcohol consumption, race/ethnicity, education, body mass index (BMI) category and history of comorbidity at baseline. All covariates had no missing values except for BMI (N = 3486), pack-years of smoking (N = 3382) and education (N = 2308) and multiple imputation method was applied for these missing values. We conducted sensitivity analyses by excluding the first two years of the follow-up period. A two-sided test was performed, and the p -value used to test statistical significance was < 0.05.

Among 117,673 participants included in this study, 116,894 (99.3%) identified themselves as omnivores, 329 (0.3%) as lacto- and/or ovo-vegetarians, 310 (0.3%) as pesco-vegetarians, and 140 (0.1%) as vegans, respectively (Table 1 ). Participants in the omnivorous diet group were more likely to smoke cigarettes and drink alcohol and less likely to have completed college education than vegetarian or vegan groups. Furthermore, omnivores had the highest average BMI (27.2 kg/m 2 ), followed by vegans (26.9 kg/m 2 ), lacto- and/or ovo-vegetarians (25.7 kg/m 2 ) and pesco-vegetarians (25.3 kg/m 2 ). The proportions of non-Hispanic white participants ranged from 57.1% in the vegan diet group to 89.2% in the omnivore diet group.

After an average follow-up of 18 years, 39,763 participants including 39,547 for omnivores, 88 for lacto- and/or ovo-vegetarian, 67 for pesco-vegetarians, and 61 for vegans were deceased (Table 2 ). After minimal adjustment (i.e., age, sex, study center locations and arms), comparing with the omnivore diet group, participants in the pesco-vegetarian group had a statistically significantly lower risk of mortality (HR [95% CI]: 0.67 [0.53–0.85]), but lacto- and/or ovo-vegetarian and vegan diet groups had no statistically significant difference in risk of mortality (HR [95% CI]: 0.88 [0.72–1.09] and 1.28 [0.99–1.64], respectively). After adjusting for all covariates, all three vegetarian diet groups had no statistically significant difference in risk of mortality. When comparing vegetarians (lacto- and/or ovo-vegetarian and vegans) with non-vegetarians (omnivores and pesco-vegetarians), risk of mortality also did not differ (HR [95% CI]: 1.01 [0.86–1.19] and 1.09 [0.93–1.28] after minimal and full adjustment, respectively). These association patterns were unchanged after excluding the first two years of the follow-up period (data not shown).

In this prospective analysis of a previous cancer-screening cohort of middle-aged and older adults in the US, over 99% of the participants self-identified as non-vegetarian and the rest followed lacto- and/or ovo-vegetarian, pesco-vegetarian or vegan diets. Pesco-vegetarians had a lower mortality risk than omnivores and vegans, which lost statistical significance after further adjusting for lifestyle and sociodemographic factors and comorbidity. We observed no difference in risk of all-cause mortality between vegetarian and non-vegetarian diets.

Previously, observational studies reported that vegetarian diets were associated with a lower risk of chronic diseases (e.g., CVD and type 2 diabetes) and their risk factors (e.g., obesity, blood lipid profiles and glucose control), compared with omnivorous diets; however, findings were less clear in terms of all-cause mortality [ 3 , 4 ]. Comparing with omnivores, no difference in risk of mortality among vegans and lacto- and/or ovo-vegetarians were reported in all three previous studies [ 8 , 11 , 12 ]. For pesco-vegetarians, comparing with omnivores, the Adventist Health Study 2 reported a statistically significant inverse association (0.81 [0.69–0.94]) [ 12 ], but not the other study (0.79 [0.59–1.06]) [ 11 ]. Although the comparison was with regular meat eaters, instead of omnivores as in our and other previous studies, in the Oxford Vegetarian/Oxford- European Prospective Investigation into Cancer and Nutrition (EPIC) Study, the risk of mortality did not differ from vegans, lacto- and/or ovo-vegetarians or pesco-vegetarians [ 8 ]. Furthermore, previous six studies compared risk of mortality between vegetarians and non-vegetarians. Three studies of Seventh-Day Adventists—the Adventist Mortality Study and Adventist Health Study 1 and 2—reported an inverse association [ 12 , 16 ], but other three previous studies reported no significant association [ 9 , 10 , 11 ]. Altogether, our null finding is consistent with the previous studies of vegetarianism and all-cause mortality, except for cohort studies of Adventists.

Differences in associations may be due to the fact that self-identified vegans in our study might have differed in chronic diseases and their risk factors from those of previous studies targeting vegetarians such as Adventist studies. The high prevalence of comorbidities and BMI in the vegan group compared with the Adventist and other previous studies, in which vegans had the lowest average BMI among the diet groups [ 12 , 17 ], may indicate that our self-identified vegans recently switched to a vegan diet because of health concerns. In our questionnaire, vegetarianism questions only pertained to the past 12 months, lacking the information on the specific duration of following vegetarian/vegan diets. In the previous pooled analysis of five prospective studies, participants who have followed a vegetarian diet for > 5 years had a lower risk of all-cause mortality than omnivores (0.93 [0.79–1.09]), but those followed ≤ 5 years had an increased risk (1.20 [1.04–1.38]) [ 16 ]. In addition, smoking and alcohol drinking were far more common in our study than Adventist Health Study 2 (9.3% vs. 1.1% for current smokers and 72.0% vs 10.1% for alcohol drinkers, respectively). Given that the PLCO study was conducted in a general, non-vegetarian population and same association patterns persisted after excluding the first two years of the follow-up period, the potentially shorter duration of following vegetarian/vegan diets might not have been sufficiently long enough for our study participants to have the typical health benefits associated with vegetarian/vegan diets.

Strength of this study is its prospective collection of diet and other important confounders with a relatively long follow-up (18 years) of death and vital status. In addition, our study is the first study conducted in a general, non-vegetarian population in the US to investigate associations between vegetarianism and mortality. A potential limitation, however, is low proportions of vegans/vegetarians in our study population (0.7%), which was lower than a previous report (1.9%) [ 18 ], but higher than another (0.4%) [ 19 ]. In addition, the self-identified vegetarian diet status was based on two questions regarding foods they excluded from their diet. Because of this, a possibility of misclassifications for each diet group cannot be fully ruled out, as reported previously on discrepancies between self-identified vegetarianism and their food and beverage consumption [ 20 ]. Classifying vegetarian diet status based on food and beverage consumption is beyond the scope of this study and warrants further investigation. Furthermore, we did not have information on the duration of vegetarian diets, which was reported to modify the direction of associations with mortality [ 16 ]. Due to the very small number of deaths in vegans and vegetarians, we were unable to conduct cause-specific nor subgroup analyses. Lastly, physical activity information at baseline was not collected and we were unable to adjust in our analyses.

In conclusion, we found no difference in risk of all-cause mortality by self-identified vegetarian diet status. Similar to previous studies, our vegetarians attained more education, were less likely to smoke cigarettes and drink alcohol, and had a lower BMI; however, vegans had higher comorbidities and similar BMI to omnivorous participants, suggesting that they likely recently switched to vegans because of health concerns. Future studies of vegetarian diets and mortality need to be conducted in general populations and consider the duration of following vegetarian diets.

Abbreviations

Body mass index

Cardiovascular disease

Diet History Questionnaire

European Prospective Investigation into Cancer and Nutrition study

Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial study

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The authors thank the National Cancer Institute (NCI) for access to NCI's data collected by the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial. The statements contained herein are solely those of the authors and do not represent or imply concurrence or endorsement by NCI.

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Keeley Blackie

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Conceptualization, K.B. and Y.T.; Methodology, K.B., G.B. and Y.T.; Formal Analysis, Y.T.; Writing—Original Draft Preparation, K.B. and Y.T.; Writing—Review and Editing, G.B. and Y.T.; Supervision, Y.T.; Project Administration, Y.T. All authors reviewed the manuscript.

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Blackie, K., Bobe, G. & Takata, Y. Vegetarian diets and risk of all-cause mortality in a population-based prospective study in the United States. J Health Popul Nutr 42 , 130 (2023). https://doi.org/10.1186/s41043-023-00460-9

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Vegetarianism may be in the genes, study finds

Allison Aubrey

Lots of factors influence what we eat, everything from taste preferences, to budgets and culture. New research suggests genetics may also play a role. Manjunath Kiran/AFP via Getty Images hide caption

Lots of factors influence what we eat, everything from taste preferences, to budgets and culture. New research suggests genetics may also play a role.

People are motivated to try a vegetarian diet for different reasons – from ethical and religious, to potential health and environmental benefits. But many people have a hard time sticking with it. In fact studies show many self-reported vegetarians actually do consume some animal products.

"A lot of people who want to be vegetarian are perhaps not able to," says Dr. Nabeel Yaseen , of Northwestern University Feinberg School of Medicine. "We wanted to know if genetics is part of the reason," he says.

Yaseen and his collaborators compared the DNA of about 330,000 people, using data from the UK Biobank initiative. The study included 5,324 vegetarians, who had not eaten any animal flesh or products derived from animal flesh for at least one year.

They found 34 genes that may play a role in adhering to a strict vegetarian diet. And they identified 3 genes that are more tightly linked to the trait.

"What we can say is that these genes have something to do with vegetarianism," Yaseen says. "Perhaps vegetarians have different variants of these genes that make them able to pursue a strict vegetarian diet," he explains. The study is published i n PLOS ONE , a peer-reviewed science journal.

Deciphering the genetic role is not exactly an easy riddle to solve. Humans have thousands of genes and there are millions of tiny variations in DNA building blocks, known as single nucleotide polymorphisms (SNPs,) where you can see differences between individuals.

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To identify SNPs that are statistically associated with the particular trait of adhering to a vegetarian diet, Yaseen and his colleagues did a genome-wide association study .

"You're looking for markers in the genome, basically trying to see if a certain trait tracks with a certain region of the genome," explains Yaseen. When they found a SNP associated with vegetarianism, they looked to see the genes around it in the same area.

Of the three genes most strongly associated with vegetarianism, the authors say two of them (known as NPC1 and RMC1) have important functions in lipid – or fat – metabolism. The study can't answer exactly how genetic differences could shape or influence vegetarians, but Dr. Yaseen has some ideas.

"One hypothesis – which is highly speculative – is that maybe there's a lipid nutrient, or nutrients, in meat that some people need and others don't," he says.

Lots of factors influence what we eat, everything from our taste preferences, to our budgets to our culture. So, the idea that food choice is also influenced by genetics is not surprising, Yaseen says.

But this is just the first step. He says more research is needed to determine which genes – and which variants – may be critical.

Yaseen points out the current study is limited to white Caucasian participants. "Ethnicity is a confounding factor," he says. For example, if the study had included people from India, where vegetarianism is more common, you might see genes or SNPs that are associated with being Indian rather than being a vegetarian.

How to eat more like a vegetarian — even if you're not one

The idea that some people might find it easier to follow a vegetarian diet due to genetic predisposition is interesting, says Christopher Gardner , a food scientist at Stanford University. And he points out that people don't need to go completely vegetarian to see benefits.

He points to research that shows impacts on human health and planetary health would be significant, even if people just decreased the amount of meat they eat each week.

"There is clearly an important benefit – and probably more realistic benefit – of reducing meat without cutting it out completely," Gardner says.

This story was edited by Jane Greenhalgh

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Going vegetarian? The dietary choice may be influenced by your genes.

Being vegetarian may be (partly) in your genes, a new study suggests. 

By analyzing the genomes of more than 335,000 people and using questionnaires to assess their meat intake, scientists have identified one point in the human genome — rs72884519 on chromosome 18 — that is significantly associated with following a vegetarian diet . In a separate analysis, the researchers identified three gene variants — NPC1, RMC1, and RIOK3 — clustered in that same region that are linked to vegetarianism, as well as another 31 genes elsewhere in the genetic code that may have a "possible role" in this dietary choice. 

It is unclear how these genes may influence people's choice to be vegetarian or the underlying physiology behind it. However, the findings, published Wednesday (Oct. 4) in the journal PLOS One , provide a taste of how genetics might partially determine the food we put on our plates.

"These results open the door for future studies that could determine which gene variants play an important role in vegetarianism and how they influence dietary choices," lead study author Dr. Nabeel Yaseen , a professor of pathology at the Northwestern University Feinberg School of Medicine, told Live Science in an email. 

Related: What's the difference between veganism vs vegetarianism

People choose to be vegetarian for many reasons, including religion, culture, ethics and environmental and health concerns. What people decide to eat is shaped not only by personal taste but also by metabolism and how different foods affect the body, all of which are influenced by genetics. Although studies have shown that genes can impact the foods we like , the possible ties between genetics and vegetarianism are poorly understood. 

In the new study, scientists compared the genomes of 5,325 vegetarians with those of 329,455 non-vegetarians using data from the U.K. Biobank , a large repository of health and genetic data from adults in the U.K. To define these categories, the researchers used two questionnaires that asked people to recount their food intake over the past year and over 24-hour periods. Vegetarians were defined as people who avoided eating animal flesh or products derived from it, such as lard. 

The study didn't directly examine how the gene variants linked to vegetarianism could influence people's dietary decisions, but the authors have a few hypotheses.

For example, several of the genes, including NPC1 and RMC1, are involved in lipid, or fat metabolism and brain function. This "raises the possibility that the ability to pursue a vegetarian diet may be influenced by lipid metabolism and its effects on the brain," Yaseen told Live Science. For example, NPC1 is involved in trafficking large lipids called complex lipids into cells, and these large fats are crucial for the development and function of the nervous system, the authors wrote. 

The study does have a few important caveats. The authors only looked at one population of white people in the U.K., and they relied on participants self-reporting what they recalled eating. This study design may impact how well the results apply to other populations and undermine the reliability of the findings. 

Joanne Cole , an assistant professor of biomedical informatics at the University of Colorado who was not involved in the research, told Live Science that she and her team also found that the rs72884519 genomic region is linked to meat consumption , in that gene variants there seem associated with a person's liking for and intake of meat.

But she also pointed out that the new study found differences in lifestyle and environmental factors between vegetarians and meat-eaters — for example, vegetarians were more likely to be women, younger, have a lower socioeconomic status and a lower body mass index (BMI), an indirect measure of body fat. So it's possible that, rather than influencing people's food choices directly, the potential vegetarian-associated genes flagged in the study instead exert their effects indirectly through these other factors, Cole said.

More work is needed to truly understand how this genomic region is linked to dietary intake, Cole added, and Yaseen noted the same: 

"We hope that future research will shed further light on the physiology of vegetarianism and enable us to provide better, personalized dietary recommendations and produce better meat substitutes," he told Live Science.