The most definitive effects on incidence of depression were found with the Mediterranean diet in a meta-analysis of 41 studies.

Healthy diets are promoted as an important part of prevention and treatment for various medical conditions (e.g., cardiovascular and cerebrovascular disorders, cancer). These researchers performed a meta-analysis of 41 observational studies, 20 of which were longitudinal, to examine whether adherence to various healthy diets was associated with a lower incidence of depression in generally healthy people.

High adherence to three of four diets studied (Mediterranean diet, Healthy Eating Index, and Dietary Inflammatory Index) was associated with lower incidence of depression. The strongest evidence was for high adherence to the Mediterranean diet and the Dietary Inflammatory Index, each with four longitudinal studies showing lower relative risks for depression incidence (0.67 and 0.76, respectively). Associations with Healthy Eating Index adherence were confined to cross-sectional studies.