Meat and mental health: a systematic review of meat abstention and depression, anxiety, and related phenomena

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DOI: 10.1080/10408398.2020.1741505
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Abstract
Objective: To examine the relation between the consumption or avoidance of meat and psychological health and well-being. Methods: A systematic search of online databases (PubMed, PsycINFO, CINAHL Plus, Medline, and Cochrane Library) was conducted for primary research examining psychological health in meat-consumers and meat-abstainers. Inclusion criteria were the provision of a clear distinction between meat-consumers and meat-abstainers, and data on factors related to psychological health. Studies examining meat consumption as a continuous or multi-level variable were excluded. Summary data were compiled, and qualitative analyses of methodologic rigor were conducted. The main outcome was the disparity in the prevalence of depression, anxiety, and related conditions in meat-consumers versus meat-abstainers. Secondary outcomes included mood and self-harm behaviors. Results: Eighteen studies met the inclusion/exclusion criteria; representing 160,257 participants (85,843 females and 73,232 males) with 149,559 meat-consumers and 8584 meat-abstainers (11 to 96 years) from multiple geographic regions. Analysis of methodologic rigor revealed that the studies ranged from low to severe risk of bias with high to very low confidence in results. Eleven of the 18 studies demonstrated that meat-abstention was associated with poorer psychological health, four studies were equivocal, and three showed that meat-abstainers had better outcomes. The most rigorous studies demonstrated that the prevalence or risk of depression and/or anxiety were significantly greater in participants who avoided meat consumption. Conclusion: Studies examining the relation between the consumption or avoidance of meat and psychological health varied substantially in methodologic rigor, validity of interpretation, and confidence in results. The majority of studies, and especially the higher quality studies, showed that those who avoided meat consumption had significantly higher rates or risk of depression, anxiety, and/or self-harm behaviors. There was mixed evidence for temporal relations, but study designs and a lack of rigor precluded inferences of causal relations. Our study does not support meat avoidance as a strategy to benefit psychological health.
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Critical Reviews in Food Science and Nutrition
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Meat and mental health: a systematic review of
meat abstention and depression, anxiety, and
related phenomena
Urska Dobersek, Gabrielle Wy, Joshua Adkins, Sydney Altmeyer, Kaitlin
Krout, Carl J. Lavie & Edward Archer
To cite this article: Urska Dobersek, Gabrielle Wy, Joshua Adkins, Sydney Altmeyer, Kaitlin
Krout, Carl J. Lavie & Edward Archer (2020): Meat and mental health: a systematic review of meat
abstention and depression, anxiety, and related phenomena, Critical Reviews in Food Science and
Nutrition, DOI: 10.1080/10408398.2020.1741505
To link to this article: https://doi.org/10.1080/10408398.2020.1741505
© 2020 The Author(s). Published with
license by Taylor and Francis Group, LLC
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Published online: 20 Apr 2020.
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REVIEW
Meat and mental health: a systematic review of meat abstention and
depression, anxiety, and related phenomena
Urska Dobersek
a
, Gabrielle Wy
b
, Joshua Adkins
a
, Sydney Altmeyer
a
, Kaitlin Krout
a
, Carl J. Lavie
c
, and
Edward Archer
d
a
Department of Psychology, University of Southern Indiana, Evansville, Indiana, USA;
b
Department of Criminology and Criminal Justice,
University of Maryland, College Park, Maryland, USA;
c
John Ochsner Heart and Vascular Institute, Ochsner Clinical School, The University of
Queensland School of Medicine, New Orleans, Louisiana;
d
Research and Development, EvolvingFX, Jupiter, Florida, USA
ABSTRACT
Objective: To examine the relation between the consumption or avoidance of meat and
psychological health and well-being.
Methods: A systematic search of online databases (PubMed, PsycINFO, CINAHL Plus, Medline, and
Cochrane Library) was conducted for primary research examining psychological health in meat-
consumers and meat-abstainers. Inclusion criteria were the provision of a clear distinction between
meat-consumers and meat-abstainers, and data on factors related to psychological health.
Studies examining meat consumption as a continuous or multi-level variable were excluded.
Summary data were compiled, and qualitative analyses of methodologic rigor were conducted.
The main outcome was the disparity in the prevalence of depression, anxiety, and related
conditions in meat-consumers versus meat-abstainers. Secondary outcomes included mood and
self-harm behaviors.
Results: Eighteen studies met the inclusion/exclusion criteria; representing 160,257 participants
(85,843 females and 73,232 males) with 149,559 meat-consumers and 8584 meat-abstainers (11
to 96 years) from multiple geographic regions. Analysis of methodologic rigor revealed that the
studies ranged from low to severe risk of bias with high to very low confidence in results. Eleven
of the 18 studies demonstrated that meat-abstention was associated with poorer psychological
health, four studies were equivocal, and three showed that meat-abstainers had better outcomes.
The most rigorous studies demonstrated that the prevalence or risk of depression and/or anxiety
were significantly greater in participants who avoided meat consumption.
Conclusion: Studies examining the relation between the consumption or avoidance of meat and
psychological health varied substantially in methodologic rigor, validity of interpretation, and
confidence in results. The majority of studies, and especially the higher quality studies, showed
that those who avoided meat consumption had significantly higher rates or risk of depression,
anxiety, and/or self-harm behaviors. There was mixed evidence for temporal relations, but study
designs and a lack of rigor precluded inferences of causal relations. Our study does not support
meat avoidance as a strategy to benefit psychological health.
KEYWORDS
Anxiety; depression; meat;
mental health; self-harm;
vegan; vegetarianism
Introduction
Background
Vegetarianism for ethical or religious reasons predates
modern history (Leitzmann 2014; Spencer 1995; Whorton
1994). Yet the common practice of abstaining from animal
flesh in the pursuit of health per se is a recent phenomenon
that began in the nineteenth and early twentieth centuries
(Porphyry 1823; Roe 1986; Whorton 1994). Given that a
century ago nutrition science was in its infancy, the earliest
arguments for the superiority of meat-freediets for health
were shaped more by religious and moral sentiments than
by empirical evidence (Whorton 1994). Nevertheless, as
investigations of human nutrition and disease expanded in
the twentieth century, vegetarianism for health gained scien-
tific credibility to augment its traditional moral and ethical
status (Rosenfeld 2018; Ruby 2012).
However, in the past few decades, research on the health
effects of meat-abstention has become increasingly contra-
dictory. For example, despite the fact that animal products,
such as red meat (e.g., beef or lamb), provide a wide range
of essential nutrients and bioactive substances (Neumann
et al. 2003,2007; Williams 2007), researchers reported
potential health benefits associated with avoiding meat and
CONTACT Urska Dobersek udobersek@usi.edu Department of Psychology, University of Southern Indiana, Evansville, IN 47712, USA.
Supplemental data for this article can be accessed at https://doi.org/10.1080/10408398.2020.1741505
ß2020 The Author(s). Published with license by Taylor and Francis Group, LLC
This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/Licenses/by-nc-nd/4.
0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in
any way
CRITICAL REVIEWS IN FOOD SCIENCE AND NUTRITION
https://doi.org/10.1080/10408398.2020.1741505
that vegetarian diets may be used to prevent or treat disease
(Kahleova, Levin, and Barnard 2018; Key et al. 1999; Singh,
Sabat
e, and Fraser 2003; Tong et al. 2019; Viguiliouk et al.
2019). As a consequence, the 2016 Position Statement of the
Academy of Nutrition and Dietetics stated, appropriately
planned vegetarian, including vegan, diets are healthful,
nutritionally adequate, and may provide health benefits for
the prevention and treatment of certain diseases(Melina,
Craig, and Levin 2016, 1970).
In contrast, while it is well-established that the mortality
of vegetarians compares positively with the general popula-
tion (Appleby et al. 2016; Appleby and Key 2016), several
reports demonstrated that there were no differences in mor-
tality when vegetarians were compared to meat-consumers
with similar socio-demographic characteristics (Appleby
et al. 2016; Appleby and Key 2016; Chang-Claude et al.
2005). Thus, while some studies are suggestive of a reduc-
tion in mortality associated with vegetarianism, the larger
body of evidence suggests that the health benefits associated
with vegetarianism may not be due to the avoidance of meat
per se, but other lifestylefactors associated with socio-eco-
nomic status, such as adequate levels of physical activity
(Archer, Lavie, and Hill 2018a), low alcohol and drug con-
sumption (OKeefe et al. 2018), or the avoidance of
tobacco products.
Moreover, and in contrast to the positive associations
between health and vegetarianism (Appleby and Key 2016;
Dinu et al. 2017; Singh, Sabat
e, and Fraser 2003; Viguiliouk
et al. 2019), recent results suggest that individuals who
abstain from meat and/or other animal-based foods may
suffer from nutritional deficiencies (e.g., vitamins B
12
and D,
x-3 fatty acids, calcium, iron, and zinc; Craig 2010; Dwyer
1991) with concomitant poorer physical health (Appleby
et al. 2007; Burkert et al. 2014b; Cofnas 2019; Iguacel et al.
2019). Furthermore, there is an emerging body of evidence
that meat-abstention is linked to mental disorders (Perica
and Dela
s2011; Young and Conquer 2005) and poorer psy-
chological well-being (Baines, Powers, and Brown 2007;
Hibbeln et al. 2018; Matta et al. 2018; Michalak, Zhang, and
Jacobi 2012; Nezlek, Forestell, and Newman 2018; Rosenfeld
2018). Specifically, when compared to those who consume
meat, vegetarians are more likely to suffer from or be diag-
nosed with major depression (Baines, Powers, and Brown
2007; Hibbeln et al. 2018; Jacka et al. 2012) and anxiety
(Baines, Powers, and Brown 2007; Bas, Karabudak, and
Kiziltan 2005), and are more likely to attempt self-harm
(e.g., suicide) (Baines, Powers, and Brown 2007; Neumark-
Sztainer et al. 1997; Perry et al. 2001).
However, the evidence linking vegetarianism with mental
disorders is not unequivocal. In 2010 and 2015, investigators
found that with respect to some facets of mental health
assessment, vegetarians were healthier than meat-consumers
(Beezhold et al. 2015; Beezhold, Johnston, and Daigle 2010).
Equivocal results and public health
Recently, Johnston et al. (Johnston et al. 2019) and Carroll
and Doherty (Carroll and Doherty 2019) suggested that the
evidence supporting public health recommendations to limit
or eliminate meat consumption was based on questionable
research and inappropriate analyses(Carroll and Doherty
2019, 767). This debate and the ever-increasing body of con-
trasting and conflicting results represent a challenge for
both clinicians and public policy architects. Yet more
importantly, equivocal and potentially biased research on
meat-consumption has contributed to the growing confusion
and incredulousness surrounding the value of nutrition sci-
ence (Archer and Lavie 2019a,2019b; Archer, Lavie, and
Hill 2018b; Archer, Pavela, and Lavie 2015; Rowe and
Alexander 2017).
The extant literature suggests that there are numerous
factors that may explain the contradictory associations of
meat-abstention and health. These include variations in
research design, recruitment and sampling strategies (Baines,
Powers, and Brown 2007; Matta et al. 2018; Michalak,
Zhang, and Jacobi 2012), the disparity between self-reported
and actual dietary intake (Archer, Marlow, and Lavie 2018d;
Archer, Pavela, and Lavie 2015), the lack of validity of
assessment protocols or metrics employed for exposures and
outcomes (e.g., diagnosed conditions vs. subjective percep-
tions), and lack of understanding and control for confound-
ing variables and/or effect modifiers.
Another important and oft-cited factor is the definition
and characterization of vegetarians and/or those who abstain
from meat consumption (Baines, Powers, and Brown 2007;
Timko, Hormes, and Chubski 2012). For example, the com-
prehensive term vegetarianmay be used to describe indi-
viduals who avoid only red meat (e.g., beef), avoid both red
and white meat (e.g., pork, poultry) or those who simply
consume predominantly plant-based diets. Furthermore,
investigators frequently subdivide vegetarians into several
groups categorized by the types of foods they exclude. While
no definition is definitive and categories vary significantly,
vegansexclude all foods and beverages derived from ani-
mals (e.g., fish, eggs, dairy, or meat) and may also avoid
using any animal-based products (e.g., leather clothing).
Ovo-lacto vegetarians consume no meat but will eat eggs
and dairy, whereas pescatarians eat fish but not red meat or
poultry, and flexitarians consume a predominantly plant-
based diet while occasionally consuming meat. These
inconsistent and intersecting definitions in concert with self-
reported dietary status may lead to misclassification because
there is a clear and important distinction between merely
reporting that one avoids meat and actual meat-abstention.
In other words, from a scientific perspective, it is clear that
self-reported dietary intake is not the equivalent of actual
dietary intake (Archer, Lavie, and Hill 2018b; Archer,
Marlow, and Lavie 2018d; Archer, Pavela, and Lavie 2015).
Meat-abstention and mental health: the need for clarity
In 2017, the World Health Organization (WHO) reported
that mental illness was the leading cause of disability world-
wide (WHO 2017), and has a major impact on cardiovascu-
lar diseases (i.e., the leading cause of mortality globally;
Lavie et al. 2016;OKeefe, OKeefe, and Lavie 2019). The
2 U. DOBERSEK ET AL.
WHO investigators estimated that over 300 million people
suffered from depression (4.4% of the global population)
and over 260 million people (3.6% of the global population)
suffered from anxiety (Friedrich 2017; Kessler et al. 2005).
These estimates reflected a substantial increase in the num-
ber of people living with mental disorders and illnesses over
the past two decades (Lancet 2015; WHO 2017).
Given the global increase in psychological disorders
(Lancet 2015; WHO 2017) in concert with increments in the
advocacy and practice of vegetarianism (Leitzmann 2014;
Statista 2019; Willett et al. 2019), there is a need to clarify
the relation between meat-abstention and psychological
health. Nevertheless, in addition to the inconsistent classifi-
cation of vegetarians in research settings, there are limita-
tions to the extant definitions and data on psychological
outcomes. For example, the WHO defines mental health as
a state of well-being in which every individual realizes his or
her own potential, can cope with the normal stresses of life,
can work productively and fruitfully, and is able to make a
contribution to her or his community(WHO 2019). While
this broad characterization provides a goal for individuals
and the societies in which they live, it is extremely limited
in its research and practical applications. More importantly,
while some investigators examining diet-disease relations
rely on physician-diagnosed disorders based on criteria from
the Diagnostic and Statistical Manual of Mental Disorders
(DSM-V; APA 2013; e.g., see (Michalak, Zhang, and Jacobi
2012)), others rely exclusively on self-reported mental health
or subjective scales with untested validity. These conceptual
and measurement issues lead to classification errors,
ambiguous findings, and limited cross-study analyses.
Given the inconsistent and contradictory nature of the
extant research, the objective of this systematic review was
to formally but concisely identify the outcomes, strengths,
limitations, and flaws in the scientific literature on the rela-
tion between the consumption or avoidance of meat and
mental health, with a focus on depression, anxiety, and a
limited number of secondary variables (e.g., self-harm). To
avoid inconsistent definitions of vegetarianism, our analysis
sought to capture studies that clearly differentiated between
individuals who reported consuming meat and those report-
ing to be meat-abstainers, while acknowledging that the
overall dietary patterns exhibited by both groups (and most
humans) are varied.
Methods
Search strategy
Five online databases (PubMed, PsycINFO, CINAHL Plus,
Medline with full text, and Cochrane Library) were searched
using a broad set of keywords for primary research that
examined psychological health in meat-consumers and
meat-abstainers. The search included all papers published up
to and including March 2019. The keywords and search
strategy can be found in Supporting Information. The search
strategy was created by the lead investigator; and two, two-
person teams independently conducted the searches. Titles
and abstracts of potentially relevant articles were
independently identified and screened by both teams. The
search strategy included examining reference lists from pre-
vious reviews and research papers. Initial search results were
imported into reference-managing software (EndNote X9,
Clarivate Analytics, 2019).
After duplicate articles were excluded, full texts of poten-
tially relevant articles were obtained and critically assessed
by both two-person teams and the lead investigator working
independently. After this assessment, the teams and lead
investigator met to arrive at a consensus on the inclusion/
exclusion criteria for each paper (e.g., psychological assess-
ment, strict definitions of dietary intake, etc.). Disputes were
adjudicated by discussion with the final decision made by
the lead investigator (UD). Consensus was obtained for all
included articles.
Study inclusion criteria
This review sought to identify primary studies that exam-
ined the relation between meat-abstention and psychological
health in humans, 1099 years of age, with a primary focus
on depression, anxiety, and a limited number of secondary
variables. This focus was necessary because many psycho-
logical outcomes are vague, difficult to quantify (e.g., disor-
dered eating, self-esteem), or are inherently biased against
individuals who do not follow current norms (e.g., vegans).
For example, in western, industrialized nations meat con-
sumption is the social and economic norm. Therefore, the
non-normative dietary exclusions espoused by vegans and
strict vegetarians may lead to inflated or illusory rates of
psychological dysfunction. For example, it is well-established
that vegetarianism may be used as a strategy to mask disor-
dered eating and that the endorsement of vegetarianism is
highest in females with severe eating pathology (Klopp,
Heiss, and Smith 2003; Zuromski et al. 2015). Given this
evidence, self-reported vegetarianism per se has been posited
to be a proxy for mental illness (Klopp, Heiss, and Smith
2003). Thus, we chose not to include outcomes that were
less well-defined or difficult to quantify such as personality
characteristics (e.g., neuroticism), or disordered eating and
related phenomena (e.g., orthorexia), to achieve more defini-
tive results and conclusions on the relation between meat-
consumption and mental health.
All study designs were eligible (e.g., cross-sectional, retro-
spective, prospective, case control, randomized controlled
trial (RCT), longitudinal). Studies were included if (1) they
were written in English language, (2) the authors provided a
clear distinction between participants who reported eating
meat (i.e., meat-consumers; e.g., omnivores) and those who
avoided meat consumption (i.e., meat-abstainers; e.g.,
vegans, vegetarians), and (3) included data on psychological
health. Given the heterogeneity of definitions of vegetarian-
ism or meat-avoidance, at times it was necessary to contact
the authors of a particular study to gain further clarification.
Our goal was to create a comprehensive, yet rigorous and
concise review. The eligible psychological outcomes were
divided into primary and secondary categories based on the
CRITICAL REVIEWS IN FOOD SCIENCE AND NUTRITION 3
frequency with which they were examined in the relevant
literature (Text Box 1).
Study exclusion criteria
Non-English studies were excluded, and studies examining
meat consumption as a continuous or multi-level variable
were excluded due to the failure of food frequency question-
naires (FFQs) and other self-report methods to accurately
quantify actual dietary intake (Archer, Hand, and Blair 2013;
Archer, Lavie, and Hill 2018b; Archer, Marlow, and Lavie
2018d; Archer, Pavela, and Lavie 2015; Schoeller et al. 2013).
Data extraction
Data extraction was conducted by both teams. The informa-
tion extracted included study characteristics (e.g., citation,
design, population, number of participants, age, etc.), psy-
chological health outcomes, definition of meat-consumers/
meat-abstainers, and key findings. The reviewers were not
blinded and had full access to paper details, such as authors,
affiliations, and journals during data extraction and compil-
ation. The extraction tables were examined for accuracy and
completeness by the lead investigator (UD). Once compiled,
information from the selected studies was transferred to
an Evidence Summary Table(Table 1).
Methodologic rigor: risk of bias assessment and
limitations
Quality assessments in systematic reviews necessitate the
critical appraisal of multiple factors and domains within and
between the included studies. To reduce the potential for
biases in the appraisal process, final adjudication, and com-
munication of results, reviewersjudgments must be inde-
pendent and constrained via a standardized protocol. As
such, each study included in our review was assessed for
methodologic rigor via qualitative critiques and quantitative
analyses of the risk of bias, validity of interpretation, and
confidence in findings by two investigators. These investiga-
tors worked independently while employing a 100-point
scale of predetermined criteria that was specifically devel-
oped for this review via an amalgam of multiple tools and
checklists (Hong et al. 2018; Weightman et al. 2004).
Specifically, each study was evaluated for design, sam-
pling and recruitment biases, specification of outcome (i.e.,
dietary and psychological assessments), analysis of outcome
(e.g., statistical design), validity of interpretation and com-
munication of results (e.g., were the conclusions supported
by the results). The 100-point scale used herein provided a
standard procedure for both the evaluative process and sub-
sequent communication of results while allowing the exten-
sibility necessary to accommodate the interdisciplinary
nature of the research question and the heterogeneity across
the studies (Please see Supporting Information).
The studies were ranked and placed in five categories
based on their score. Higher scores indicated greater meth-
odologic rigor: scores 90100 indicated high rigor, low risk of
bias, and high confidence in results; scores 6089 indicated
moderate rigor and risk of bias, and modest confidence in
results; scores 4059 indicated a moderate-to-high risk of
bias, and moderate-to-low rigor and confidence in results;
scores 2039 indicated a high risk of bias, and low rigor and
confidence in results; and scores 019 indicated a severe risk
of bias and very low rigor and confidence in results.
Results
Description of studies
The initial search resulted in 7102 potentially relevant
articles. After de-duplication, the tiles and abstracts of 6840
papers were screened for inclusion/exclusion criteria.
This resulted in 100 full-text articles which were read fully
and critically assessed. This qualitative analysis resulted in
18 papers that met the inclusion/exclusion criteria. These
included 16 cross-sectional, 1 mixed cross-sectional and
longitudinal study, and 1 RTC. The total sample included
160,257 participants (85,843 females and 73,232 males) with
149,559 meat-consumers and 8584 meat-abstainers from
geographic regions including Europe, Asia, North America,
and Oceania. The sample sizes ranged from 38 to 90,380
participants with an age-range from 11 to 96 years. The
articles were published from 1997 to January 2019.
As per PRISMA statement (Preferred Reporting Items for
Systematic Review and Meta-Analyses; Moher et al. 2009),
results from each stage of the review are displayed in Figure 1.
Table 1 provides a summary of the studies included
in the review in alphabetical order.
Methodologic rigor analysis
The results of the critical appraisal of methodologic rigor and
concomitant confidence in results as well as significant strengths,
limitations, and flaws are presented in Supporting Information.
Analyses revealed that the studies ranged from high to low rigor
with high to very low confidence in results, respectively. Results
are presented in rank-order of rigor beginning with the most
rigorous study. Inter-class correlations between reviewers were
very high (ICC ¼0.978; 95% CI: 0.9420.992, p<.001).
General critique
The studies were placed in five categories based on their
score for methodologic rigor. Two of the 18 selected studies
had a low risk of bias; 5 had moderate risk; 4 had
moderate-to-high risk; 4 had a high risk, and 3 studies had
Text Box 1. Included psychological outcomes.
Primary outcomes
1. Depression or depressive symptoms/disorders
2. Anxiety or anxiety-related symptoms/disorders
Secondary outcomes
3. Deliberate self-harm (e.g., attempted suicide)
4. Mood/stress perception
5. Affective well-being/Quality of life (QoL)
4 U. DOBERSEK ET AL.
Table 1. Summary table.
Citation and study design
Participants (sample size,
population, and setting)
Psychological health outcome
(description/scale/measure)
þþ
Definition of vegetarian
sample and comparison group Key findings
Baines et al. (2007). Public
Health Nutrition, 10(5),
436442 Cross-sectional
9113 Australian women
between 22 and 27 years
of age
The Medical Outcomes Study
Short Form Health Survey
SF-36.
Vegetarians (n¼252) excluded
red meat, poultry, and fish;
semi-vegetarians excluded red
meat (n¼827); Non-
vegetarians (n¼8034) ate
red meat.
Vegetarians and semi-
vegetarians had poorer
mental health, higher
depression and anxiety
related symptoms, and
greater rates of self-harm
than non-vegetarians.
Bas et al. (2005). Appetite,
44(3), 309315
Cross-sectional
1205 students from Turkey;
597 females and 608 males
between 17 and 21
years (M
age
¼21.3)
The Social Physique Anxiety
Scale (SPAS), and the
State-Trait Anxiety
Inventory (STAI)
Are you a vegetarian?Yes/No
Vegetarians (n¼31), non-
vegetarians (n¼1174).
Female vegetarians scored
significantly higher on the
STAI than female non-
vegetarians.
Beezhold et al. (2015).
Nutritional Neuroscience.
2015;18(7):289296
Cross-sectional
620 adults from USA; 487
females and 133 males
between 25 and 60 years
of age (M
age
¼34.83)
The Depression Anxiety Stress
Scale-21 (DASS)
Vegans: consumed no animal
foods (n¼283). Vegetarians:
consumed only eggs or dairy
(n¼109). Omnivores:
consumed meat, poultry, or
fish (n¼228).
Vegans reported significantly
lower anxiety and stress
and scored significantly
lower on total DASS 21
compared to omnivores.
Beezhold et al. (2010).
Nutrition Journal, 9, 26
Cross-sectional
138 Seventh Day Adventists
from USA 77 females and
61 males (M
age
¼43.04)
DASS and the Profile of Mood
States (POMS)
Vegetarians: excluded all flesh
foods (n¼60);
Omnivores (n¼78).
Vegetarians reported
significantly better mental
health (lower scores on the
DASS and the POMS)
than omnivores.
Beezhold and Johnston,
(2012). Nutrition Journal,
11, 9 Randomized
control trial
39 adults from USA; 32
females and 7 males; age
not reported
The DASS and POMS Vegetarians: avoided all animal
foods except dairy (n¼13).
þþ
Fish eaters: consumed fish,
avoided eating meat and
poultry (n¼13). Omnivores:
consumed meat and/or
poultry (n¼13).
Vegetarians reported
significantly better mood
than omnivores and fish
eaters after the trial.
Boldt et al. (2018). Journal of
the International Society of
Sports Nutrition, 15(1), 33
Cross-sectional
281 European endurance
runners; 159 females and
122 males (M
age
¼40)
The World Health
Organization Quality of Life
Assessment - Brief
(WHOQLA-Brief)
Vegetarians/vegans: excluded
animal products such as
meat, fish, dairy products,
eggs, and honey (n¼158).
Omnivores: no dietary
restrictions (n¼123).
No significant differences in
QoL between vegetarians/
vegans and omnivores.
Forestell and Nezlek (2018).
Ecology of Food Nutrition,
57(3), 246259
Cross-sectional
6450 USA undergraduate
students; 3707 females
and 2715 males between
16 and 47
years (M
age
¼18.96)
The Center for Epidemiologic
Studies Depression Scale
(CES-D)
Vegetarians: restricted all meat
and fish products (n¼276).
Omnivores: regularly ate fish
and/or meat (n¼4955).
Vegetarians had significantly
higher CES-D scores
than omnivores.
Hibbeln et al. (2018). Journal
of Affective Disorders, 225,
1317 Cross-sectional
9668 male partners of English
women in early stages of
pregnancy; age categories
(<25 to 35þ)
The Edinburgh Postnatal
Depression Scale
How many times nowadays do
you eat?followed by 17
categories of foods Yes/Never
Vegetarian/vegan (n¼350)
Omnivore (n¼9318)
Vegetarians had significantly
higher depression scores
than non-vegetarians.
Lavallee et al. (2019). Journal
of Affective Disorders, 248,
147154 Cross-sectional,
longitudinal
22,417 adults from Germany,
Russia, USA, and China;
13,006 females and 8596
males; (M
age
¼39.10)
The DASS and the Positive
Mental Health scale
Are you currently vegetarian?
Yes/No Vegetarians: excluded
meat and/or fish (n¼3400).
Non-vegetarians: included
meat (n¼18,603).
Cross-sectional: Vegetarian
diet related to higher
levels of depression and
anxiety among Chinese
students. Longitudinal:
Vegetarian diet was
predictive for depression
and anxiety in
Chinese students.
Lindeman (2002). Ecology of
Food and Nutrition, 41(1),
7586 Cross-sectional
308 women from Finland; age
13 to 74 (M
age
¼29)
CES-D Vegetarians (n¼42);
þþ
Semi-
vegetarians: avoided red meat
or only ate fish (n¼69);
Omnivores (n¼197).
Semi-vegetarians and
vegetarians had more
symptoms of depression
than omnivores.
Matta et al. (2018). Nutrients,
10(11) Cross-sectional
90,380 adults from France;
48,035 females and 42,345
males; Age: 16 to 69
years (M
age
¼42.78)
CES-D Vegans: no consumption of
animal products (n¼81).
þþ
Pesco-vegetarians
(n¼832);
þþ
Lacto-ovo-
vegetarians (n¼562).
Omnivores: consumed all
foods (n¼88,905).
The odds of depressive
symptoms increased when
meat was excluded from
the diet. The prevalence of
depressive symptoms
increased with the number
of excluded food groups.
Michalak et al. (2012).
International Journal of
Behavioral Nutrition and
Physical Activity, 9, 67
Cross-sectional
4181 German adults; 2233
females and 1883 males;
age: 18 to 65
(M
age
¼38.87), and a socio-
demographically matched
subsample of non-
vegetarians (n¼242)
The Munich Composite
International Diagnostic
Interview (mental disorder)
Do you currently follow a
vegetarian diet (no meat) or
did you follow a vegetarian
diet in the past?Answers:
no, never,”“yes, completely,
or yes, predominantly.
þþ
Vegetarians (n¼54), and
non-vegetarians (n¼3872)
Vegetarians displayed
elevated prevalence rates
for depressive and anxiety
disorders in both full and
matched subsample.
(continued)
CRITICAL REVIEWS IN FOOD SCIENCE AND NUTRITION 5
a severe risk of bias. The quality of the study appeared to
affect the outcome of the study.
There were numerous issues that reduced the confidence
in the published results. As detailed in our discussion, these
issues included cross-sectional design, non-representative
sampling, biased recruitment, the use of subjective (i.e., self-
reported) dietary and psychological data, the failure to
account for social desirability and observer-expectancy
effects (e.g., reactivity), the failure to collect data on actual
dietary intake, and statistical, interpretive, and communica-
tion errors such as the failure to correct for multiple com-
parisons, recognize regression to the mean, and the
inappropriate use of causal language.
Summary of results
Primary outcomes: depression, anxiety, and
related symptoms
Fourteen of the 18 studies examined depression, anxiety,
and/or related symptoms (see Table 2). Independent of
methodologic rigor, 7 of the 14 studies found a higher
prevalence or risk in participants who avoided meat con-
sumption (Baines, Powers, and Brown 2007; Forestell and
Nezlek 2018; Hibbeln et al. 2018; Lindeman 2002; Matta
et al. 2018; Michalak, Zhang, and Jacobi 2012; Stokes,
Gordon, and DiVasta 2011), 3 studies found no group dif-
ferences (Beezhold and Johnston 2012; Perry et al. 2001;
Timko, Hormes, and Chubski 2012), 2 studies demonstrated
mixed results (e.g., higher rates in females only; Bas,
Karabudak, and Kiziltan 2005; Lavallee et al. 2019), and 2 of
the 14 studies found a higher prevalence or risk in meat-
consumers (Beezhold et al. 2015; Beezhold, Johnston, and
Daigle 2010;Table 2). The four most rigorous studies dem-
onstrated that the prevalence or risk of depression and/or
anxiety (or related symptoms) was significantly greater in
participants who avoided meat consumption (Baines,
Powers, and Brown 2007; Hibbeln et al. 2018; Matta et al.
2018; Michalak, Zhang, and Jacobi 2012). The results of the
five least rigorous studies were less clear; two studies
demonstrated that meat-consumers had a higher risk or
prevalence of depression and anxiety (Beezhold et al. 2015;
Beezhold, Johnston, and Daigle 2010), one study found no
group differences (Beezhold and Johnston 2012), and two
Table 1. Continued.
Citation and study design
Participants (sample size,
population, and setting)
Psychological health outcome
(description/scale/measure)
þþ
Definition of vegetarian
sample and comparison group Key findings
Neumark-Sztainer et al.
(1997). Archives of
pediatrics and adolescent
medicine;151(8):833838
Cross-sectional
321 adolescents matched on
age, sex, and ethnicity
drawn from a larger
population in Minnesota;
261 females and 60 males;
age: 12 to 20 years
Health compromising
behaviors assessed with
a 6-point Likert-type scale
ranging from never to
daily.
Single item: Have you ever
tried to kill yourself?
Are you on a special diet
because of being a
vegetarian?Cross-checked
with FFQ.
Vegetarians (n¼107), non-
vegetarians (n¼214)
Vegetarians had a greater
prevalence of reported
suicide attempts compared
to non-vegetarians.
Perry et al. (2001). Journal of
Adolescent Health, 29(6),
406416
Cross-sectional
4746 USA adolescents;
2255 females and 2265
males; age 11 to 18
years (M
age
¼14.9)
Depressive symptoms
assessed on a 7-item
standardized scale
Are you a vegetarian?Yes/No
Vegetarians (n¼262), non-
vegetarians (n¼4258)
Vegetarians were more likely
to think about killing
themselves and ever tried
to kill [themselves]than
non-vegetarians.
Pfeiler and Egloff (2018).
Appetite, 120, 246255
Cross-sectional
Study 1: 4496 German adults;
2351 females, 2145 males;
age: 17 to 96 years
(M
age
¼51.84)
Study 2: 5125 German adults;
2669 females, 2409
males (M
age
¼52.42)
Study 1 and 2: Affective
well-being, life satisfaction
(three and single item,
respectively)
Study 1 (n
1
) andStudy 2 (n
2
):
Vegans: no animal product
(n
1
¼13, n
2
¼28).
Vegetarians: no meat and
avoided fish (n
1
¼110;
n
2
¼278); meat-eaters
(n
1
¼4373, n
2
¼4819).
No significant differences
between the groups in
either study on affective
well-being or life
satisfaction.
Stokes et al. (2011). 63.
Journal of Adolescent
Health, 48(2), S50
Cross-sectional
38 female adolescents
meeting the DSM-IV
criteria for anorexia
nervosa (AN); (M
age
¼16.5)
The Beck Depression
Inventory (BDI) and
the STAI
Vegetarians: no consumption of
any form of meat (via author
correspondence); Vegetarians
(n¼17), non-vegetarians
(n¼21);
Vegetarians with AN reported
higher anxiety and trended
toward higher levels of
depression than non-
vegetarians with AN.
Timko et al. (2012). Appetite,
58(3), 982990
Cross-sectional
486 USA university students;
374 females and 111 males;
age: 18 to 40þ
years (M
age
¼24.90
The DASS Vegans: excluded animal
products (n¼35).
Vegetarians: ovo-, lacto- or lacto-
ovo vegetarian (n¼111)
þþ
Semi-vegetarians: consumed
no red meat or pork (n¼75).
Omnivores: ate meat (n¼265)
No significant differences
between the groups on
depression, stress,
and anxiety.
Wirnitzer et al. (2018).
Nutrients, 11(1).
Cross-sectional
245 endurance runners from
German-speaking countries;
141 females and 104 males
(median age: 3740)
Stress perception: Are you
under pressure and/or are
you suffering from stress?
Yes/No
Vegans: rejected all products
from animal sources (n¼91).
Vegetarians: no meat (n¼45).
Omnivores: no dietary
restrictions (n¼109).
No differences between the
groups on stress
perception.
þþ
The term semi-vegetarianwas defined differently across the studies. When the term was used to describe meat-abstainers, the group was included in our
analyses. If semi-vegetarianincluded occasional meat consumers, the group was not included in our analyses.
Discrepancies between the total sample of participants and the diet groups.
Discrepancies between the total sample of participants and the number of males/females.
Note: AN: Anorexia Nervosa; SF: short form; BDI: The Beck Depression Inventory; CES-D: The Center for Epidemiologic Studies Depression Scale; DASS: The
Depression Anxiety Stress Scale; FFQ: Food Frequency Questionnaire; SPAS: The Social Physique Anxiety Scale; STAI: The State Trait Anxiety Inventory; POMS:
The Profile of Mood States; QoL: Quality of Life; WHOQLA: The World Health Organization Quality of Life Assessment.
6 U. DOBERSEK ET AL.
found that meat-consumers had a lower risk or prevalence
(Lindeman 2002; Stokes, Gordon, and DiVasta 2011).
The most rigorous study reviewed, Michalak, Zhang, and
Jacobi (2012), found a clear relation between the avoidance
of meat and depression and anxiety in both a representative
sample of German adults (n¼4181; including 3872 non-
vegetarians and 54 complete vegetarians) and a socio-
demographically matched subsample of non-vegetarians
(n¼242). Meat-abstainers (i.e., complete vegetarians) had
1-month, 12-month, and lifetime prevalence of unipolar
depressive disorders of 7.4%, 24.1%, and 35.2%, respectively.
Conversely, the prevalence was substantially lower in meat-
consumers: 6.3%, 11.9%, and 19.1% in the full sample,
and 5.0%, 10.3%, and 20.7% in the matched sample. When
comparing the complete vegetariansto the matched non-
vegetarians,the Odds Ratios for 1-month, 12-month, and
lifetime prevalence were 1.53 (95% CI: 0.484.95); 2.75 (95%
CI: 1.305.82); and 2.09 (95% CI: 1.103.95), respectively.
As the authors stated, Prevalence rates of the complete vege-
tarians are nearly 15%higher than of the non-vegetarians
(Michalak, Zhang, and Jacobi 2012, 5).
The 1-month, 12-month, and lifetime prevalence of
anxiety disorders for meat-abstainers was 20.4%, 31.5%, and
31.5%, respectively. As with their results for depression, the
prevalence in meat-consumers was significantly lower:
10.7%, 17.0%, and 18.4% in the full sample and 8.7%, 13.2%,
and 15.3% in the matched sample. When comparing the
complete vegetariansto the matched non-vegetariansthe
Odds Ratios for 1-month, 12-month, and lifetime prevalence
were 2.69 (95% CI: 1.125.99), 3.02 (95% CI: 1.525.98),
and 2.55 (95% CI: 1.304.99), respectively. The authors
wrote, Prevalence rates for anxiety disorder were especially
high (more than twice as high) in the completely vegetarian
group than in the non-vegetarian matched group(Michalak,
Zhang, and Jacobi 2012, 5).
Similarly, the results from the largest and second most
rigorous study in the review by Matta et al. (2018)foundthat
in an extremely large, nationally representative sample of
French adults (n¼90,380), 28.4% of meat-abstainers had
symptoms of depression, whereas only 16.2% of meat-consumers
did. The odds of having depressive symptoms increased when
meat was excluded from the diet (Matta et al. 2018).
Consistent with the more inclusive studies of Michalak,
Zhang, and Jacobi (2012) and Matta et al. (2018), the largest
study of women exclusively, Baines, Powers, and Brown
(2007;n¼9113) and the largest study of men exclusively,
Hibbeln et al. (2018;n¼9668), found a greater risk or
prevalence of depression (Hibbeln et al. 2018) and depres-
sion and anxiety (Baines, Powers, and Brown 2007) in meat-
abstainers. One particular strength of Baines et al.s analysis
was the inclusion of multiple assessments of psychological
outcomes, including reports of prior diagnoses of depression
Records identied through database
searching
(n = 7099)
Screening
Included Eligibility Idenficaon
Additional records identied
through other sources
(n = 3)
Records after duplicates removed
(n = 6840)
Records screened
(n = 6840)
Records excluded (via
title/abstract)
(n = 6740)
Full-text articles assessed
for eligibility
(n = 100)
Articles excluded (no separate
groups = 40, outcome irrelevant =
23, in Spanish = 1, registered trials
= 4, clinician report = 2, meta-
analysis = 12)
Studies included in
qualitative synthesis
(n = 18)
Figure 1. PRISMA flow-chart: search results.
CRITICAL REVIEWS IN FOOD SCIENCE AND NUTRITION 7
or anxiety and the use of prescription medications. They
found that the use of prescription medications for depres-
sion in women who abstained from meat was nearly twice
that of women who ate meat (8.0% vs. 4.2%).
In contrast to the majority of the literature, in 2010
Beezhold, Johnston, and Daigle (2010;n¼138) showed that
meat-abstainers reported less depression and anxiety than
meat-consumers, and in 2015, Beezhold et al. (2015;
n¼620) showed that meat-abstainers reported less anxiety
than meat-consumers. The potential reasons for these
contradictory findings are detailed in Supporting
Information and our discussion.
Secondary outcomes (Table 3)
Ten of the 18 studies examined the secondary outcomes of
self-harm, mood, stress perception, affective well-being, and
QoL (Table 3). In contrast to the clear results on depression
and anxiety, three studies found no differences between
groups (Boldt et al. 2018; Pfeiler and Egloff 2018; Wirnitzer
et al. 2018), three favored meat-abstainers (Beezhold et al.
2015; Beezhold and Johnston 2012; Beezhold, Johnston, and
Daigle 2010), three studies favored meat-consumers (Baines,
Powers, and Brown 2007; Neumark-Sztainer et al. 1997;
Perry et al. 2001), and one study provided mixed results
(Lavallee et al. 2019).
Self-harm
Three studies examined self-harm behaviors. Baines, Powers,
and Brown (2007) found that in a large, representative
sample Australian women (n¼9113), the prevalence of
deliberate self-harm was over three times greater in meat-
abstainers than meat-consumers (10.0% vs. 3.1%). Similarly,
in a large sample of US adolescents (n¼4746), Perry et al.
(Perry et al. 2001) found that suicide attempts were more
than twice as prevalent in meat-abstainers compared to
meat-consumers (18.3% vs. 8.6%), and the prevalence of sui-
cide ideation (i.e., thinking about killing oneself) was 34.7%
in meat-abstainers versus 24.9% in meat-consumers.
Similarly, in a matched subsample of adolescents (n¼321)
that was part of a larger study, Neumark-Sztainer et al.
(Neumark-Sztainer et al. 1997) found that suicide attempts
Table 2. Primary outcomes.
Prevalence or risk of depression and anxiety, or related symptoms
Confidence in results Favored meat-consumers (total n¼143,760)
No significant differences
(total n¼28,893)
Favored meat-abstainers
(total n¼758)
High Michalak et al. (2012) (Depression and Anxiety)
High Matta et al. (2018) (Depression)
Moderate Baines et al. (2007) (Depression and Anxiety)
Moderate Hibbeln et al. (2018) (Depression)
Moderate Bas et al. (2005) (Anxiety: Females) Bas et al. (2005) (Anxiety: Males)
Moderate Timko et al. (2012) (Depression
and Anxiety)
Moderate-to-low Perry et al. (2001) (Depression)
Moderate-to-low Forestell and Nezlek (2018) (Depression)
Moderate-to-low Lavallee et al. (2019) (Depression and
Anxiety: China)
Lavallee et al. (2019) (Depression and
Anxiety: US, Germany, Russia)
Low Lindeman (2002) (Depression)
Low Beezhold et al. (2010) (Depression
and Anxiety)
Very low Stokes et al. (2011) (Depression and Anxiety)
Very low Beezhold et al. (2015) (Anxiety)
Very low Beezhold and Johnston (2012)
(Depression and Anxiety)
Lower prevalence or risk.
Table 3. Secondary outcomes.
Prevalence or risk of self-harm, mood/stress perception, affective well-being, and quality of life (QoL)
Confidence in results Favored meat-consumers (total n¼36,597) No significant differences (total n¼27,439) Favored meat-abstainers (total n¼797)
Moderate Baines et al. (2007) (Self-Harm)
Moderate Neumark-Sztainer et al. (1997)
(Suicide attempts)
Moderate-to-low Perry et al. (2001)
(Suicide attempts and ideation)
Moderate-to-low Pfeiler and Egloff (2018)
(Life Satisfaction and Affective Well-being)
Moderate-to-low Lavallee et al. (2019)
(Positive Mental Health: China)
Lavallee et al. (2019)
(Positive Mental Health: US, Russia, Germany)
Low Boldt et al. (2018) (QoL)
Low Wirnitzer et al. (2018) (Stress)
Low Beezhold et al. (2010) (Mood/Stress)
Very low Beezhold et al. (2015) (Stress)
Very low Beezhold and Johnston (2012) (Stress)
Lower prevalence or risk.
8 U. DOBERSEK ET AL.
were more prevalent in meat-abstainers (25%) compared to
meat-consumers (17%).
Mood and stress perception
Four studies examined mood and stress perceptions
(Beezhold et al. 2015; Beezhold and Johnston 2012;
Beezhold, Johnston, and Daigle 2010; Wirnitzer et al. 2018).
Wirnitzer et al. examined stress perceptions in a sample of
245 European endurance runners (57% female) and found
no differences between groups (Wirnitzer et al. 2018).
Conversely, Beezhold, Johnston, and Daigle (2010) examined
mood states in Seventh Day Adventists (i.e., a religious
group that espouses vegetarianism; n¼138) and found that
meat-abstention was linked to more favorable mood states
(Beezhold, Johnston, and Daigle 2010). In 2015, in a highly
selected sample in which vegetarians and vegans were sub-
stantially over-represented (i.e., 283 vegans vs. 228 meat-
consumers), Beezhold et al. found that those who abstained
from meat reported better mood and lower stress than
meat-consumers (Beezhold et al. 2015).
In 2012, Beezhold and Johnston (2012)conductedaRCTin
which 39 self-characterized omnivores (82% female) were
assigned to one of three groups: lacto-vegetarian (i.e., avoided
all animal foods except dairy), ovo-pescatarian (i.e., avoided
meat and poultry but consumed fish and eggs), or omnivore
(i.e., consumed meat and/or poultry at least once daily).
Their results suggested that restricting meat, fish, and poultry
improved some domains of short-term mood states. As detailed
in our discussion, this study had major design flaws (e.g.,
potential observer-expectancy effects) and errors in interpret-
ation and communication (e.g., nonequivalent groups at
baseline, failure to recognize regression to the mean).
Well-being and QoL
Two studies examined well-being and QoL (Boldt et al.
2018; Pfeiler and Egloff 2018). In a sample of 281 endurance
runners (57% female), Boldt et al. (2018) found that QoL
did not differ between groups (Boldt et al. 2018). Similarly,
in a large sample of 4496 German adults, Pfeiler and Egloff
(2018) found that neither affective well-being nor current
life-satisfaction differed between meat-abstainers and meat-
consumers (Pfeiler and Egloff 2018).
Primary and secondary outcomes
Table 2 presents the results of the primary outcomes,
depression and anxiety, or related symptoms in rank order
of rigor.
Discussion
Based on this systematic review comprising 160,257 partici-
pants from varied geographic regions, including Europe,
Asia, North America, and Oceania, aged 11 to 96 years, there
is clear evidence that meat-abstention is associated with
higher rates or risk of depression, anxiety, and self-harm.
The results with respect to mood states, affective well-being,
stress perception and QoL are less clear and the majority of
studies do not support unequivocal inferences.
Across all studies, there was no evidence to support
a causal relation between the consumption or avoidance
of meat and any psychological outcomes. However, three
studies provided evidence suggesting (contradictory) tem-
poral relations between meat-abstention and depression and
anxiety. Michalak, Zhang, and Jacobi (2012) demonstrated
that the mean age at the adoption of meat-abstention
(30.58 years) was substantially older than the mean age of
the onset of metal disorder (24.69 years). These authors pos-
ited that mental disorders may lead to the adoption of a
meat-less diet. The authors stated that individuals with men-
tal disorders may choose a vegetarian diet as a form of
safety or self-protective behavior(Michalak, Zhang, and
Jacobi 2012, 6) due to the perception that plant-based diets
are more healthful or because individuals with mental disor-
ders may be more aware of suffering of animals(Michalak,
Zhang, and Jacobi 2012, 2). Interestingly, these investigators
also found that people with a lifetime diagnosis of psycho-
logical disorders consumed less fish and fast food. While
these results conflict with previous research on fast food and
mental health (Crawford et al. 2011), they support Matta
et al.s results and hypothesis that the exclusion of any food
group, and especially meat and poultry, is associated
with increased odds of having symptoms of psychological
disorders (Matta et al. 2018).
Conversely, in their longitudinal analysis, Lavallee et al.
(2019) found that meat-abstention was linked to slight
increases over time(Lavallee et al. 2019, 153) in depression
and anxiety in Chinese students. One important caveat
when considering these disparate results on temporal
relations may be differences in the factors that led to meat-
abstention (e.g., religious practices, health and ethical
considerations, or socio-economic status). For example, eco-
nomically disadvantaged individuals who do not consume
meat due to its relative cost may be at risk for ill-health for
myriad reasons independent of their lack of meat consump-
tion. Thus, future research examining temporal relations
should establish clear distinctions between individuals and
populations that abstain from meat consumption due to eth-
ical, religious, and health-related perceptions, or those who
do not consume meat for economic reasons.
Strengths, limitations, and flaws of the extant literature
Psychological outcomes
The most rigorous studies used objective and/or multiple
assessments of psychological outcomes. For example,
Michalak, Zhang, and Jacobi (2012) were the first investiga-
tors to use standardized and comprehensive assessment of
mental disorders based on DSM criteria (APA 2013).
Similarly, Baines, Powers, and Brown (2007) provided mul-
tiple assessments of psychological outcomes that included
reported physician-diagnosed conditions, and the use of pre-
scription medication for depression and anxiety in concert
with self-reported symptoms and behaviors (e.g., self-harm;
Baines, Powers, and Brown 2007). Comparably, Hibbeln
CRITICAL REVIEWS IN FOOD SCIENCE AND NUTRITION 9
et al. (2018) included detailed participant histories, including
childhood contact with psychiatric services and family
history of depression. Methodologically weaker studies
employed a single questionnaire and, in some cases,
employed a single-item examining psychological symptoms
over a limited timeframe (e.g., the previous week).
Sampling
The most rigorous studies examined large, representative
and/or matched samples (Baines, Powers, and Brown
2007;Mattaetal.2018; Michalak, Zhang, and Jacobi
2012), whereas the least rigorous used biased recruitment
strategies and biased convenience sampling. For example,
Michalak, Zhang, and Jacobi (2012) employed both a
large representative sample and a socio-demographically
matched subsample for comparison. The strength of this
approach cannot be understated. Similarly, Neumark-
Sztainer et al. (1997) employed a matched sample drawn
from a much larger study population. Conversely, a num-
ber of studies attempted to over-sample vegans and vege-
tarians by directly targeting these groups via internet
sources such as social websites geared to VG and VEG
[vegan and vegetarians](Beezhold et al. 2015)andvegan
chat-rooms and/or magazines and vegetarian fairs
(Boldt et al. 2018; Wirnitzer et al. 2018). As discussed
below, these sampling strategies in concert with self-
reported data are a major design flaw.
Investigators who seek to over-sample groups that are
highly invested (e.g., ethically, socially, intellectually or emo-
tionally) in their lifestyleor dietary choices should
acquaint themselves with the large body of research on cog-
nitive dissonance (Festinger 1962), social-desirability (Fisher
1993), and observer-expectancy effects (e.g., reactivity). This
body of work is especially relevant when applied to the
errors and biases of self-reported dietary intake data; for
details, please see (Archer, Hand, and Blair 2013; Archer,
Lavie, and Hill 2018b; Archer, Marlow, and Lavie 2018c,
2018d; Archer, Pavela, and Lavie 2015; Hebert et al. 1995;
Schoeller et al. 2013). This large and well-established body
of research suggests that for individuals who maintain a
strong group identity or affinity, meat consumption or
avoidance may represent a significant ethical, intellectual,
emotional, behavioral, social and/or spiritual investment that
extends well-beyond a simple dietary choice. As such, many
individuals (e.g., Paleo and meat-onlydieters, vegans, veg-
etarians, Seventh Day Adventists) will be pre-disposed to
report significantly higher levels of physical and psycho-
logical health to avoid cognitive dissonance and remain con-
sistent with self- and/or group-appraisals.
These non-intentional biases in concert with the potential
for a participant to intentionally misreport outcomes to sup-
port his or her ideological stances or religious beliefs may
induce systematic and non-quantifiable errors when employ-
ing self-report protocols. As such, the oversampling of
groups that are highly invested in their dietary regimes for
health, religious, or ideologic concerns (e.g., animals rights)
will lead to biased recruitment and extremely unreliable data.
In fact, research on cognitive dissonance and social
desirability suggests that the greater the motivation for
adhering to ones dietary or lifestyle pattern (or self-concep-
tion), the larger the potential error induced via the use of
self-reports (Archer, Marlow, and Lavie 2018c; Festinger
1962). Future studies should employ objective data collection
protocols when over-sampling groups that may be prone to
intentional and/or non-intentional misreporting.
Assessment of dietary status (exposure)
One major limitation of all studies in this review was the use
of self-reported dietary status. Currently, there is an escalating
and contentious debate on the validity of self-reported dietary
data and the use of food frequency questionnaires in nutri-
tion (Archer and Lavie 2019b; Archer, Lavie, and Hill 2018b;
Archer, Marlow, and Lavie 2018d; Archer, Pavela, and Lavie
2015;Ioannidis2018;Mart
ın-Calvo and Mart
ınez-Gonz
alez
2018;Satijaetal.2015; Schoeller et al. 2013; Subar et al.
2015; Trepanowski and Ioannidis 2018). The debate revolves
around two major criticisms. First, critics of self-reported
data state that without objective corroboration of dietary self-
reports, it is impossible to quantify measurement error due to
intentional and nonintentional distorting factors, such as
deliberate misreporting (i.e., deception/lying), social desirabil-
ity, reactivity, misestimation, and false memories of dietary
intake (Archer, Pavela, and Lavie 2015). Second, critics argue
that pseudo-quantification (i.e., the transformation of
reported foods and beverages into estimates of nutrient and
caloric intake) created a fictional discourse on diet-disease
relations (Archer, Hand, and Blair 2013; Archer, Lavie, and
Hill 2018b). This latter argument is based on the fact that
65% of self-reported dietary data have been shown to be
physiologically implausible [i.e., respondents cannot survive
on the amount of foods and beverages reported (Archer,
Hand, and Blair 2013; Archer, Pavela, and Lavie 2015;Ferrari
et al. 2002; Goldberg et al. 1991)].
The first criticism is potentially applicable to our analy-
ses. Nevertheless, the dichotomous nature of our classifica-
tions (i.e., meat-consumers versus meat-abstainers) reduces
both its importance and impact. The second critique regard-
ing pseudo-quantification is not relevant to our review, nor
is it relevant to qualitative assessments of dietary intake.
Duration of dietary patterns
A number of studies failed to include information of the age
at which meat-abstention began or the duration of non-con-
sumption. If a relationship exists between the length of time
an individual has abstained from meat consumption and
physical or psychological health, these data are essential to
future investigations. This is especially true since the nutri-
tional deficiencies that are sometimes associated with vegan-
ism and vegetarianism may be more detrimental in children
and adolescents (Cofnas 2019) and may take years to
develop (Craig 2010; Dwyer 1991).
10 U. DOBERSEK ET AL.
Other potential confounders
Clearly, diet is not the only determinant of psychological
health (Archer 2018a,2018b). Nevertheless, a number of the
studies failed to include important potential confounders
and effect modifiers. These include race, ethnic, or religious
affiliation, social norms, as well as lifestyle behaviors that
directly affect health (e.g., smoking, and alcohol use) and
the physiologic determinants of dietary energy intake (e.g.,
physical activity, body cellularity; Archer 2018b; Archer,
Lavie, and Hill 2018a; Archer et al. 2018e). Given that when
compared to the general population, individuals who follow
a vegetarian diet tend to be more health-conscious, more
physically active, more highly educated, consume less alco-
hol, be nonsmokers and have higher socio-economic status
(Appleby et al. 2016; Appleby and Key 2016; Chang-Claude
et al. 2005), it is essential for future studies to include
detailed information on participantshealth and behavioral
histories and current characteristics.
Strengths and limitations of this review
This systematic review had several strengths, including our a
priori decision to select only studies that provided a clear
distinction between meat-consumers and meat-abstainers.
This decision allowed for a clear and yet rigorous assess-
ment. While myriad studies examined vegetarianism along a
continuum, these were excluded simply because the lack of
a clear distinction rendered inferences equivocal.
A second strength was our decision to limit our primary
outcomes to well-defined mental disorders (i.e., depression,
anxiety, and related symptoms) and a limited number of
secondary outcomes (e.g., self-harm). This focus allowed for
a concise yet rigorous review and ameliorated the effects of
poorly operationalized psychological phenomena. For
example, by excluding results on disordered eating, dietary
restraint, orthorexia, and personality (e.g., neuroticism), we
avoided the potential misclassification and concomitant
pathologizing of those who simply wish to avoid specific
foods or food groups (e.g., vegans).
Our study also had limitations. First, we excluded non-
English language studies, that could potentially bias our
results in favor of Westernnorms which include meat
consumption. For example, our selection criteria excluded
papers published in languages other than English. (e.g.,
Japanese, Hindi) and in non-English databases. Thus, our
review may have omitted studies from geographic regions
that follow predominantly vegetarian or plant-based dietary
patterns. In these areas, the relation between meat-avoidance
and psychological health may differ from Westernnations.
Nevertheless, our review included a large sample from
China; so, this limitation may be trivial.
Second, while our search was clearly defined and compre-
hensive, our criteria excluded a large number of papers that
provided data on this topic [e.g., see (Anderson et al. 2019;
Barthels, Meyer, and Pietrowsky 2018; Burkert et al. 2014a;
Cooper, Wise, and Mann 1985; Jacka et al. 2012; Larsson
et al. 2002; Li et al. 2019; Northstone, Joinson, and Emmett
2018)]. Nevertheless, we think that a highly focused review
has the potential to provide stronger evidence and, as such
is more informative to the medical, research, and lay com-
munities. Third, despite the high confidence we place in our
finding that meat-abstention is linked to psychological disor-
ders, study designs and lack of rigor precluded valid infer-
ences of temporality and causality.
Fourth, meat consumption is often inconsistently classified
in research and national surveillance settings (Gifford et al.
2017;OConnor et al. 2020)aswellasacrosslanguages.For
example, in English, the broad category of meatsubsumes
both redand whitemeat (e.g., beef and poultry). However,
in German, the term meatexcludes poultry. As such, the
results for the studies employing German samples were poten-
tially more restrictive. Finally, inferences from our results are
only as accurate as the data collected by the included studies.
Given that all studies relied on self-reported dietary status,
there is the possibility of misclassification because self-reported
dietary consumption is not the equivalent of actual dietary
consumption (Archer, Hand, and Blair 2013; Archer, Lavie,
and Hill 2018b; Archer, Marlow, and Lavie 2018c, 2018d;
Archer, Pavela, and Lavie 2015). In other words, there is an
obvious and important distinction between merely reporting
that one avoids meat and actual meat-abstention; and research
supports the fact that self-defined vegetarians and meat-
abstainers may consume meat (Haddad and Tanzman 2003).
Suggestions for future direction
Future investigators should avoid the most common flaws
detailed herein (e.g., uncorroborated self-reported data,
biased sampling, confounding, etc.). First, the limitations of
self-reported dietary data may be partially overcome with
point-of-purchase (barcode) data (Ng and Popkin 2012).
Nevertheless, while purchase data may be more objective, it
is not necessarily an accurate proxy for actual consumption.
Second, investigators must acknowledge and address the
effects of biased sampling with the use of self-reported data.
Individuals highly invested in specific dietary patterns may
be predisposed to intentional and non-intentional misreport-
ing. Third, detailed behavioral and health-related histories
and current lifestyles should be considered essential. The use
of physician-diagnosed disorders based on criteria from the
DSM-V (APA 2013) is preferable to self-reported symptoms
and would assist in producing more definitive results.
Given the results of this review, an interesting future dir-
ection would be to examine if meat consumption per se has
psychological benefits. For example, there is evidence that a
significant number of vegans and vegetarians return to meat
consumption over time and that former vegetarians and
vegans in the U.S. outnumber current meat-abstainers
(Faunalytics 2016). As such, one research question that can
be answered empirically is whether it is the nutritional prop-
erties of meat (as measured via serum biochemical analyses),
the reduced social burden or stigma associated with omni-
vory, or other physiologic or social factors that drive the
transition from meat-abstainer back to meat-consumer.
CRITICAL REVIEWS IN FOOD SCIENCE AND NUTRITION 11
Conclusion
The purpose of this review was to provide evidence to inform
both clinical practice and future research. Overall, the scientific
literature examining the relation between the consumption or
avoidance of meat and psychological health varied substan-
tially in both rigor and validity of interpretation. Higher qual-
ity studies suggested that those who abstained from meat
consumption had a greater risk or prevalence of depression,
anxiety, and self-harm. With respect to clinical practice, the
avoidance of meat may be a behavioral marker that signifies
poorer mental health. Study designs and/or a lack of rigor pre-
cluded inference of causal relations and none should be
inferred. However, our study does not support avoiding meat
consumption for overall psychological health benefits.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Funding
This study was funded in part via an unrestricted research grant from
the Beef Checkoff, through the National Cattlemens Beef Association.
The sponsor of the study had no role in the study design, data collec-
tion, data analysis, data interpretation, or writing of the report.
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14 U. DOBERSEK ET AL.
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