Healthy dietary indices and risk of depressive outcomes: asystematic review and meta-analysis of observational studies

With depression being the psychiatric disorder incurring the largest societal costs in developed countries, there is a need togather evidence on the role of nutrition in depression, to help develop recommendations and guide future psychiatric healthcare. The aim of this systematic review was to synthesize the link between diet quality, measured using a range of predefinedindices, and depressive outcomes.

Medline, Embase and PsychInfo were searched up to 31stMay 2018 for studies thatexamined adherence to a healthy diet in relation to depressive symptoms or clinical depression. Where possible, estimateswere pooled using random effect meta-analysis with stratification by observational study design and dietary score. A total of20 longitudinal and 21 cross-sectional studies were included.

These studies utilized an array of dietary measures, including:different measures of adherence to the Mediterranean diet, the Healthy Eating Index (HEI) and Alternative HEI (AHEI), theDietary Approaches to Stop Hypertension, and the Dietary Inflammatory Index. The most compelling evidence was foundfor the Mediterranean diet and incident depression, with a combined relative risk estimate of highest vs. lowest adherencecategory from four longitudinal studies of 0.67 (95% CI 0.55–0.82). A lower Dietary Inflammatory Index was alsoassociated with lower depression incidence in four longitudinal studies (relative risk 0.76; 95% CI: 0.63–0.92).

There werefewer longitudinal studies using other indices, but they and cross-sectional evidence also suggest an inverse associationbetween healthy diet and depression (e.g., relative risk 0.65; 95% CI 0.50–0.84 for HEI/AHEI). To conclude, adhering to ahealthy diet, in particular a traditional Mediterranean diet, or avoiding a pro-inflammatory diet appears to confer someprotection against depression in observational studies. This provides a reasonable evidence base to assess the role of dietaryinterventions to prevent depression.

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