Context: More than 300 million people worldwide have been diagnosed with depression, which is a leading cause of disability and disease burden. Elucidating dietary patterns that may reduce the risk of depression could help reduce the incidence of other diseases.

Data sources: PubMed/MEDLINE, ISI Web of Science, Scopus, Embase, and Google Scholar databases were searched to identify relevant publications up to May 2018.

Study selection: All observational studies that considered the Mediterranean diet as the exposure variable and depression as the main outcome or as one of the outcome variables were included in this systematic review and meta-analysis. Two authors independently screened 3229 publications. A total of 14 observational studies were included in the meta-analysis.

Data extraction: Two authors independently extracted the data and assessed the risk of bias.

Results: The studies in the meta-analysis included a total of 56 043 participants. When 5 effect sizes from 4 cohort studies were combined, no significant association was observed between adherence to the Mediterranean diet and risk of depression (overall hazard ratio = 0.95; 95%CI, 0.79-1.16). When 3 effect sizes from 3 cohort studies that reported β coefficients were combined, again no significant association was found (β = -0.00; 95%CI, -0.12, 0.12). However, when 9 effect sizes from 9 cross-sectional studies were combined, an inverse significant association was found between adherence to the Mediterranean diet and risk of depression (overall odds ratio = 0.72; 95%CI, 0.60-0.87).

Conclusions: The analysis of cohort studies revealed no significant association was found between adherence to the Mediterranean diet and risk of depression. However, an inverse significant association between adherence to the Mediterranean diet and odds of depression in cross-sectional studies.