There’s little debate about the fact that a plant-based diet is the healthiest around, both in terms of physical health and brain health. But a new study suggests that a vegetarian diet may, counterintuitively, be linked to depression. Though there are some limitations to the new research (namely, that it was in men only), there’s one reason that it may be right on: Vegetarians and vegans may be low on the vitamins, minerals and fatty acids that are essential to neurological function. So the study may at least be a good reminder to add back what you may be lacking, either with food or with supplement.
The authors, from the University of Bristol and the NIH, looked at data from 9,700 men in Britain—all were the husbands of pregnant women taking part in a long-term study on parent and child health. The men indicated whether they were vegetarian and vegan, and filled out questionnaires about the specific makeup of their typical diets.
Men who were vegetarian/vegan, of which there were only 350 total (the team lumped the two groups together, since there weren’t many vegans), were more likely to have depression than non-vegetarians, and more likely to have a higher depression score. Even after adjustment for potential confounding variables (like family history, number of children, job status, and so on), the connection still held. There was also a slight connection between the number of years one had been vegetarian and the severity of one’s depression, but that link wasn’t statistically significant.
Despite the obvious health benefits of vegetarianism, there are some good reasons that vegetarians and vegans might be prone to depression. Their intake of omega-3 fatty acids, vitamin B12 and folate may be lower than meat eaters’, the authors write, and deficiencies of these have all been associated with depression. The same may be true for iron and zinc. Additionally, the authors suggest that vegetarians may have a higher intake of omega-6 fatty acids, which have been shown to increase inflammation and have also been linked to depression. Vegetarians and vegans may also consume more plant estrogens, particularly if they eat a lot of soy products. Finally, the authors suggest that vegetarians and vegans may take in higher levels of pesticides, assuming their intake of plant-based foods is higher than average.
The team points out that reverse causation can’t be ruled out—that is, people who are already depressed might be more likely to become vegetarian, perhaps in hopes of treating their depression with diet, or because of ethical or other concerns. Studies like this don’t show causation, just correlation, so it’s hard to know which way the relationship works, or whether it’s a two-way street. The authors also suggest that it’s possible that something else altogether may be “causing” both the vegetarianism and the depression: “It is possible that for some proportion of the population,” the write, “vegetarianism is not chosen for health, religious or ethical reasons, but is a marker for other psychiatric disorders manifesting with symptoms of both eating disorders and depressive symptoms.”
Given that the study was quite small, and will need to be repeated in a much larger sample of both men and women, it’s hard to draw any real conclusions. At the very least, it may be a good reminder to take supplements (talk with your doctor first), if you’re vegetarian, and particularly if you’re vegan, since B12 comes from animal sources only. The authors cite studies finding that depression was reduced, sometimes by up to 50%, in people who started taking B6, B12, and folic acid supplements. Whether you’re veggie or not, getting all the essential vitamins, minerals, protein, and fatty acids you need is clearly key, both for physical and mental health.