Causal influence of dietary habits on the risk of major depressive disorder: A diet-wide Mendelian randomization analysis.

BACKGROUND: Extensive observational evidence links diet quality to the risk for major depressive disorder (MDD), while clinical trials show that dietary improvement can improve depressive symptoms. However, due to issues with blinding dietary trials, confirming a causal relationship for diet's influence on MDD requires further research. Thus, we systemically investigated the bi-directional causal relationships between dietary habits and MDD by using two-sample Mendelian randomization (MR). METHODS: We collected publicly available genome-wide association studies' summary statistics for dietary habits from UK Biobank (n = 449,210) and MDD from the Psychiatric Genomics Consortium (n = 142,646). We used a weighted median approach to synthesize MR estimates across genetic instruments. For the robustness of our results, we compared weighted median results with results from the inverse-variance weighted, the weighted mode, and MR-PRESSO. RESULTS: There was moderate evidence that beef intake has a protective effect on MDD. There was weak but detectable evidence that cereal intake has a protective effect on MDD, while non-oily fish intake might increase the risk of MDD. We did not observe any causal effect of MDD on dietary habits. LIMITATIONS: Our study may suffer from the violation of assumptions of MR due to horizontal pleiotropy; therefore, we did several sensitivity analyses to detect and minimize the bias. CONCLUSIONS: In this two-sample MR analysis, we observed that higher beef intake may be protective against MDD. However, MDD did not appear to affect dietary habits. Potential mechanisms need to be further investigated to support our novel findings.