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.
Not only that, but also vegan diet is literally making people crazy (or crazy people are more often on vegan diet, dealer’s choice).
Source: https://www.tandfonline.com/doi/full/10.1080/10408398.2020.1741505#abstract