A systematic review undertaken by researchers at University College, London, suggests an association between adherence to the Mediterranean diet and lower rates of depression. A total of 41 studies were included in the review. An array of dietary approaches were covered by the studies, but the most compelling link was that between the Mediterranean diet and depression. An anti-inflammatory diet was also associated with lower rates of depression.
Although the link has not yet been proven as causal, the authors speculate on possible biological mechanisms. These include the microbiome-gut-brain axis which is now believed to play a key role in neuropsychiatry.
(Healthy dietary indices and risk of depressive outcomes: a systematic review and meta-analysis of observational studies. Molecular Psychiatry, on-line 26 September 2018.)