The results caught the researchers off guard:
The researchers found the vegetarians reported diets significantly lower in EPA and DHA, the omega-3 fatty acids that we get from eating fish, and which many studies have found are a key factor in improving both physical and mental health. So they expected to find the vegetarians would have higher incidences of issues like depression, anxiety, and mood problems. Instead, they found the opposite result. Vegetarians scored lower on depression tests and had better mood profiles than their fish- and meat-eating peers.
Worth keeping in mind that the vegetarians studied are Seventh Day Adventists, who tend to eat better than other vegetarians. But it’s not like they’re the gold standard: if you do a little reading and get your B-12 and DHA, there’s no reason why you can’t eat even better than they do.
Note that the second page of this article makes an annoying recommendation to eat grass-fed rather than feedlot beef, on the grounds that doing this might provide some of the mental health benefits you’d get by going completely vegetarian. But I suspect that the key mental health benefit to being vegetarian may be the ability to clear out that lingering certainty in the back of your mind that animals are being slaughtered on your behalf. (Thanks: Naomi and Paul.) Link.