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Depression and other mental disorders

The consumption of meat and fish influences the mental health of consumers.

On November 9, 2009 in Philadelphia, the result of a study on the influence of diet on the personal well-being of the persons was published.1 For this purpose 3 groups were formed:

  • One group served as a control. The people in this group were still allowed to eat meat, as all group participants did before the investigation. 
  • The second group ate fish 3-4 times a week, but no other meat. 
  • Finally, the third group was fed lacto-vegetarian (without meat, fish and eggs) during the study.

While hardly any mood changes were observed in the first two groups, the third (vegetarian) group showed a clear change: The participants in this group were less tense and less confused. From this it can be concluded that what we eat also has an influence on our mental state.
This study is very meaningful, as the persons studied were Adventists who, in addition to the diet, had very similar living conditions.

In November 2014, another study confirmed these findings: Vegans have lower stress levels and mental health problems.2 Study participants included 283 vegans, 109 vegetarians and 228 omnivores. 

Against studies

Of course, such a result could not be left that way, so there were several follow-up studies that tried to doubt this result.
Great media attention was gained by two such studies. The first study is from 2012.3 She compared 54 vegetarians with 242 comparative people. Interesting is that of the 54 alleged vegetarians about half consumed fish.  Thus, only 26 people left, who really lived vegetarian (the consumption of milk and eggs was not collected). An evaluation of so few vegetarians inevitably results in a rather random result. In addition, it was not asked why a person lives vegetarian and whether the negative state of mind was present even before the change to the vegetarian diet. Whether the 26 vegetarians have a healthy diet or not, is not clear from the study. In particular, a deficiency of vitamin B12 can actually lead to an impairment of mental health.

Another study on this topic was published in 2017.4 Here 9668 partners of pregnant women were evaluated. Of these, 311 men described themselves as vegetarians and 39 as vegans. The number of vegans was so small that they were grouped together for the evaluation with the vegetarians. However, more than half (174 people) said that they consume fish. Even other meat was consumed by at least 37. The evaluation was thus distorted by this division into "vegetarians" and "non-vegetarians".
Again, the scientists have to admit in their summary that it is not clear whether the vegetarian diet is the cause of mental imbalance. Since the survey was made during the pregnancy of their women this could be an explanation: Especially during this time vegetarians are increasingly under stress, because they have to assert themselves against the prejudices of society and "professionals". In particular, it should be noted here that the data collection took place from 1991 to 1992. At this time, a pregnancy of vegetarians was still very much controversial, both among physicians and dieticians. Accordingly, the psychological pressure on the expectant parents was great.
Incidentally, this study did not diagnose any real depression, but only a questionnaire on the likelihood of it.

General considerations

Although it is not yet clear how the vegetarian or vegan lifestyle affects the psyche, there are some things that need to be considered:

  1. There is not a single study that would have looked at vegans - though the opposite is said repeatedly in the mass media, equating vegetarians and vegans. 
  2. The studies available today usually do not include real vegetarians (except the ones mentioned above with Adventists), as many of the participants identify themselves as vegetarians, yet often consume meat, chicken or fish.
  3. A vegetarian diet is as diverse as any other diet too: An alcoholic who mainly feeds on sweets can live vegan, but certainly not healthy. None of the studies took into account whether or not the vegetarians eat a full and varied diet. Research suggests that a diet high in vegetables and fruit positively affects the psyche.5 And every healthy vegan diet has a high percentage of vegetables and fruits. At least this should always be taken into account.
  4. An association of depression and vitamin B12 deficiency appears to be present. This could be proven at least in studies with meat eaters.6 Therefore, every study should also check the B12 status of the participants.
  5. Since the data collections are usually very old data, it must be noted that the vegetarian diet was at least as much criticized by society as the vegan one today. This constant criticism of one's own lifestyle can lead to stress and general malaise.
  6. Animal lovers who view animals as fellow creatures and not as food are often especially sensitive people, and therefore prone to psychological pressure. In addition, vegetarians / vegans are particularly concerned about animal suffering in slaughterhouses and animal factories. Even this clear view of the immeasurable animal suffering certainly does not contribute to the improvement of the state of mind.

All these aspects suggest that studies will continue to prove that vegetarians are more stressed or depressed. Often these are random results that the media likes to take up. And even if the result was indeed scientifically tenable, that does not mean that it would directly correlate with nutrition. So far, no causal relationship between vegetarian diet and psyche has been found.

Renato Pichler

  1. Beezhold BL, Johnston CS, Daigle DR. Restriction of flesh foods in omnivores improves mood: a pilot randomized controlled trial. Poster presented at: American Public Health Association's 137th Annual Meeting and Exposition; November 9, 2009: Philadelphia, PA.

  2. Beezhold B, Radnitz C, Rinne A, DiMatteo J.: Vegans report less stress and anxiety than omnivores. Nutr. Neurosci. 2014 November 21.

  3. Johannes Michalak, Xiao Chi Zhang, Frank Jacobi: Vegetarian diet and mental disorders: results from a representative community survey, Int J Behav Nutr Phys Act. 2012; 9: 67.

  4. Joseph R. Hibbeln, Kate Northstone, Jonathan Evans, Jean Golding: Vegetarian diets and depressive symptoms among men, Journal of Affective Disorders, Vol. 225, Pages 13-17. Online erschienen: Juli 2017.

  5. Alan C Tsai, Tsui-Lan Chang, Shu-Hwang Chi: Frequent consumption of vegetables predicts lower risk of depression in older Taiwanese – results of a prospective population-based study, Volume 15, Issue 6, June 2012 , pp. 1087-1092.
    Jun S Lai, Sarah Hiles, Alessandra Bisquera, Alexis J Hure, Mark McEvoy, John Attia: A systematic review and meta-analysis of dietary patterns and depression in community-dwelling adults, Am J Clin Nutr 2014;99:181–97.

  6. Penninx, B.W., Guralnik, J.M., Ferrucci, L., Fried, L.P., Allen, R.H., Stabler, S.P., 2000. Vitamin B(12) deficiency and depression in physically disabled older women: epidemiologic evidence from the women's Health and Aging Study. Am. J. Psychiatry 157, 715–721.

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