Meat-Free Diets and Mental Health

Early in 2023 a new study was published that examined the relationship between consuming a meat-free diet and mental health issues such as depression and anxiety.  Multiple evidence has illustrated the connections between the foods we eat and their impacts on our physical health, but research results on the effects of different foods on mental health is less certain. (1)

This research gathered its participants through an on-line question presented on Instagram, Twitter and Youtube asking the following; “Is a meat-free diet (vegan or vegetarian) related to poor mental health and disordered eating behaviors? Or vice versa?”  This led to an on-line questionnaire in which those interested self-identified as consumers of either a meat-free diet or an omnivore diet and answered other questions regarding age, gender, height and weight, education level, marital status, current physical or psychiatric disorders, whether they smoked or drank alcohol, how much they exercised and their satisfaction with their own physical appearance.  Invitations to participate in the study were posted to those between the ages of 18 and 65 who were eating either a diet completely free of meat (vegetarian or vegan) or an omnivore diet.  Multiple participation was prevented by placing a “cookie” on their browsers when participants submitted a response. (1)

The study ended up with 1,355 participants, 836 of them eating a vegan or vegetarian diet and 519 of them eating an omnivore diet.  Two other on-line questionnaires were then employed to collect further data from the participants (1);

• HADS (Hospital Anxiety and Depression Scale) – a 14-question self-report on their own levels of anxiety and depression.
• TFEQ-R21 (Three-Factor Eating Questionnaire) – assesses eating behaviours such as restrained eating (dieting), emotional eating and uncontrolled eating.

Results of the analysis of the collected data indicated that people eating a diet free of meat were significantly associated with less anxiety and depressive symptoms, less dieting, less emotional eating and less uncontrolled eating when compared with people consuming an omnivore diet.  8.3% of those in the omnivore diet group were not satisfied with their physical appearance compared with 4.2% of those eating the meat-free diet.  (1)

In their discussion, the researchers examine the possible mechanisms that might be causing this relationship between diet and mental health.  They point out that emotional stress has been associated with increased oxidative damage and a rise in the prevalence of depression and anxiety.  Diets low in animal-sourced foods and high in plant-sourced foods are inherently high in healthy nutrients like fiber, vitamins and minerals as well as in phytochemicals and antioxidants that reduce chronic inflammation and oxidative stress.  Chronic inflammation has been established as a causing factor of mental disorders such as depression and anxiety.  Plant-sourced foods also encourage the growth of beneficial microbes in the gut thereby improving communication between the brain and the gut.  (1)

This research has some interesting findings but it does have limitations.  Because of its cross-sectional design that analyzes data from a population at a single point in time, this study cannot establish a causal link between diet types and mental health disorders.  In addition, self-reported data necessitates good recall and the willingness to be truthful about what they have been eating from participants, a requirement that is often not met.  Finally, this investigation was accomplished completely on-line with no oversight or lab measurements to corroborate the food intake data being supplied by the study participants. (1)

However, other previous research does back up this study by illustrating the substantial effect that food choices can have on human mental outlook. Here is a sampling of some of them.

2009 science published in the British Journal of Psychiatry analyzed the dietary patterns and incidence of depression in 3,486 participants over a five-year period and found that those eating more whole foods exhibited fewer symptoms of depression than those who ate mostly processed foods (2).

A 2010 cross-sectional study on 138 Seventh Day Adventists illustrated that vegetarian eaters had significantly better scores than omnivores on the Depression Anxiety Stress Scale (DASS), a standardized measurement of mood (3).  The researchers noted that vegetarians have lower intake of the long-chain omega-3 fatty acids, DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid), which can decrease inflammation.   However, the intake of AA (arachidonic acid) by vegetarians is also low and so they avoid the inflammatory by-products of the metabolism of AA (4).

A 2010 analysis from Japan assessed the dietary patterns and symptoms of depression of 521 municipal employees.  Those eating the highest amounts of vegetables, fruit, mushrooms and soy products had 60% fewer depressive symptoms than those eating the lowest quantity of these foods (5).

In 2010 and 2015 volunteers recruited from among employees of Geico, a major insurance corporation, were entered into a study of the effects of a worksite nutrition program for improved health and productivity.  More than 400 participants with a BMI of 25 or more or a diagnosis of type-2 diabetes were involved in the two trials of this study with their five months of follow-up.  Subjects were divided into two groups, one of which received weekly instruction on a low-fat vegan diet and the other who received no dietary intervention.  The vegan group experienced improvements significantly greater than those of the control group.  These included an increase in general health, mental health and emotional well-being; less depression, anxiety and fatigue; decreased food costs; and increased overall diet satisfaction.  The vegan group also reported a 40 to 46% decrease in health-related productivity impairments at work and at home.  (6,7)

A meta-analysis from 2017 looked at eight observational studies, three cohort studies and two case-control studies and found that meat consumption is associated with a moderately higher 13% increased incidence of depression. (8)

In 2017 the SMILES Trial in Australia looked at whether improving the diets of people with major depression would improve their mood.  This was a randomized controlled trial that provided seven individual nutritional consulting sessions delivered by a clinical dietician to half the participants and a social support session of the same length to the other half of participants.  After 12 weeks those who improved their diet with the help of a dietician showed much higher improvements in ratings on a depression scale than those in the social support only control group (9).

The SMILES Trial was followed in late 2017 by a larger study.  In this trial adults with depression were randomized into two groups; the interventional group received food hampers with Mediterranean diet ingredients, cooking workshops and fish oil supplements every two weeks for 6 months while the control group simply attended a social group every two weeks for three months.  At the end of three months the participants following the enhanced diet were eating many more vegetables, legumes, fruits, nuts and whole grains and less red meat, chicken and unhealthy snacks.  They showed greater reduction in depression and improved mental health overall compared to the control group.  These benefits were sustained after 6 months (10).

In July of 2018 the results of a meta-analysis from the United Kingdom were released.   This review looked at eleven studies published between 1999 and 2017 that had examined the health effects for diabetics of eating a plant-based or vegan diet.  Results showed that type-2 diabetics eating either vegan or plant-based had much better outcomes than the control subjects eating a more standard diet. Symptoms of depression were considerably lower.  Levels of hemoglobin A1c, a marker of lack of diabetes control, was reduced by over 3.5 times and fasting blood glucose levels dropped twice as much as that of the controls.  The healthy diet group also reduced both total and LDL cholesterol, lost about twice as much weight as those on the control diet and drastically reduced their requirement for blood pressure lowering medications (11).

In September of 2018 a systematic review of 41 scientific studies that had looked at the link between diet quality and depression was undertaken.  Results showed that a diet rich in fruits, vegetables, whole grains and legumes and avoiding processed meat, dairy and trans-fats could reduce risk of depression by 35%.   On the other hand, diets that included high amounts of processed meats and trans-fats increased the risk of depression.  Researchers suggested that a healthy diet reduces both inflammation and insulin resistance, both of which can have positive effects on mental state.  They also stated that the antioxidants found in plants may be helping to regulate emotions (12).

Another trial in 2023, this one coming from the UK, used data from the UK Household Longitudinal Study which ran between 2010 and 2017, following the same individuals over time.  It determined that both mental and physical well-being improves as the quantity and frequency of fruit and vegetable consumption increases.   (13)

Contrarily, a study from 2021 that was widely distributed on-line reported opposite results.  However, it was “funded in part via an unrestricted research grant from the Beef Checkoff, through the National Cattlemen’s Beef Association” and its results were skewed towards the meat industry (14,15).  The authors of the 2023 on-line study emphasize the importance of further, more-balanced investigations into the relationship between diet types and mental health.  (1).

Keep all this in mind as you choose the foods you provide to your body as fuel.  Remember that fruits like a juicy orange or a perfectly ripe pear make great snacks.  Consider that you can get all the protein you need from consuming a wide variety of plant-sourced foods.  Beans and lentils are particularly good sources of protein.  Recognize that the brightly coloured fruits and vegetables that make up the attractive displays in your local grocery store are advertising their bountiful content of phytochemicals and antioxidants, definitely nutrients that your body needs for optimal health.  Such foods are the makings of a happier, healthier state of mind.

 

SOURCES:

1  Şentürk, E., Güler Şentürk, B., Erus, S., et. al. Is meat-free diet related to anxiety, depression and disordered eating behaviors? A cross-sectional survey in a Turkish sample. Annals of Medical Research. 2023;30(5): 569-575. Doi:10.5455/annalsmedres.2023.01.026.

2  Akbaraly, T.N., Brunner, E.J., Ferrie, J.E., Marmot, M.G., Kivimaki, M., Singh-Manoux, A.  Dietary pattern and depressive symptoms in middle age. Br J Psychiatry. 2009; 195:408-413.

3  Beezhold, B.L., Johnston, C.S., Daigle, D.R. Vegetarian diets are associated with healthy mood states: a cross-sectional study in seventh day adventist adults. Nutr J. 2010;9:26.

4  Farooqui, A.A., Horrocks, L.A., Farooqui, T.  Modulation of inflammation in brain: a matter of fat. J Neurochem. 2007, 101: 577-599.

5  Nanri, A., Kimura, Y., Matsushita, Y., Ohta, M., Sato, M., Mishima, N., Sasaki, S., Mizoue, T.  Dietary patterns and depressive symptoms among Japanese men and women. Eur J Clin Nutr. 2010 Aug; 64(8):832-839.

6  Katcher, H.I., Ferdowsian, H.R., Hoover, V.J., Cohen, J.L., Barnard, N.D. A worksite vegan nutrition program is well-accepted and improves health-related quality of life and work productivity.  Ann Nutr Metab. 2010; 56(4):245-252.

7  Agarwal, U., Mishra, S., Xu, J., Levin, S., Gonzales, J., Barnard, N.D.  A multicenter randomized controlled trial of a nutrition intervention program in a multiethnic adult population in the corporate setting reduces depression and anxiety and improves quality of life: the GEICO study.  Am J Health Promot. 2015 Mar-Apr; 29(4):245-254.

8 Zhang, Y., Yang, Y., Xie, M.-S., Ding, X. et al. Is meat consumption associated with depression? A meta-analysis of observational studies.  Springer Nature.  December 2017.  BMC Psychiatry; 17(1): 409.  Doi:10.1186/s12888-017-1540-7.

9 Jacka, F.N., O’Neil, A., Opie, R., Itsiopoulos, C., Cotton, S., Mohebbi, M., Castle, D. et al.  A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial).  BMC Medicine 2017; 15:23

10 Parletta, n.,  Zarnowiecki, d., Cho, j., Wilson, A., Bogomolova, S., Villani, A.  A Mediterranean-style dietary intervention supplemented with fish oil improves diet quality and mental health in people with depression: A randomized controlled trial (HELFIMED).  Nutritional Science; Published online 07 Dec 2017.  https://doi.org/10.1080/1028415X.2017.1411320.

11 Toumpanakis, A., Turnbull, T., Alba-Barba, I.  Effectiveness of plant-based diets inpromoting well-being in the management of type 2 diabetes: a systematic review.  BMJ Open Diab Res Care 2018; 6: e000534. doi:10.1136/bmjdrc-2018-000534.

12 Lassale, C., Batty, G.D., Baghdadli, A., Jacka, F., Sánchez-Villegas, A., Kivimäki, M., Akbaraly, T.  Healthy dietary indices and risk of depressive outcomes: a systematic review and meta-analysis of observational studies.   Mol Psychiatry. 2018 Sep 26. doi: 10.1038/s41380-018-0237-8.

13  Ocean, N., Howley, P., Ensor, J. Lettuce be happy: a longitudinal UK study on the relationship between fruit and vegetable consumption and well-being. Soc Sci Med. 2019;222:335-345. Doi:10.1016/j.socscimed.2018.12.017.

14  Dobersek, U., Wy, G., Adkins, J., Altmeyer, S., Krout, K., Lavie, C.J., Archer, E.  Meat and mental health: a systematic review of meat abstention and depression, anxiety, and related phenomena. Critical Reviews in Food Science and Nutrition; 61:4, 622-635, Doi: 10.1080/10408398.2020.1741505.

15  https://www.insider.com/study-does-not-say-meat-eating-improves-mental-health-2020-5