Aim: To systematically examine the longitudinal observational evidence between diet and the incidence of depression in adults aged 45 years and older.

Method: Three electronic databases were searched for cohort studies published up to December 2020 that investigated the association between baseline dietary intake and incidence of depression in community-dwelling adults aged 45+years. Combined odds ratios (OR) and 95% confidence intervals (95%CI) were calculated. Random-effects models were used.

Results: In total 33 articles were included, with 21 combined in meta-analyses. Both the Dietary Inflammatory Index and the Western diet were associated with an increased odds of incident depression (Dietary Inflammatory Index: OR 1.33; 95%CI 1.04, 1.70; P = 0.02; Western: OR 1.15 95%CI 1.04, 1.26; P = 0.005). Higher fruit and vegetable intakes were associated with a reduced risk of incident depression (vegetables: OR 0.91; 95%CI 0.87, 0.96; P < 0.001; fruit: OR 0.85; 95%CI 0.81, 0.90; P < 0.001). No association was observed between the Mediterranean diet, "healthy" diet, fish intake and incident depression.

Conclusions: Results suggest an association between higher consumption of pro-inflammatory diets and Western diets and increased incidence of depression, while higher intake of fruit and vegetables was associated with decreased incidence of depression. These results are limited by the observational nature of the evidence (results may reflect residual confounding) and the limited number of studies. More high-quality intervention and cohort studies are needed to confirm these associations and to extend this work to other food groups and dietary patterns.