The most thorough research found that meat-avoiders (i.e., "full vegetarians") had a 7.4%, 24.1 %, and 35.2% 1-month, 12-month, and lifetime prevalence of unipolar depressive disorders, respectively. In contrast, meat consumers had a much lower prevalence: 6.3%, 11.9%, and 19.1%.
Similarly, the 1-month, 12-month, and lifetime prevalence of anxiety disorders for meat abstainers were much higher at 20.4%, 31.5%, 31.5%, and 10.7%, 17.0%, and 18.4% in the meat eaters respectively.
https://pmc.ncbi.nlm.nih.gov/articles/PMC10027313/#:~:text=The%20most%20thorough%20research%20found,11.9%25%2C%20and%2019.1%25.