Meat Consumption and Depression: An Updated Systematic Review and Meta-Analysis

Background: Several original studies have reported an inconsistent association between low meat consumption (e.g., vegetarian diets) and the risk of depression. The aim of this study was to quantify the relationship between low meat consumption and depression, identifying possible sources of heterogeneity and the potential role of psychosocial variables. Methods: A systematic review and meta-analysis were performed and reported according to PRISMA guidelines through a comprehensive search in Medline, Web of Science, Scopus, and PsychInfo databases from inception to January 2024 (PROSPERO registration ID: CRD42023405426). The exposures analyzed were (1) a meat-free diet and (2) a flexitarian (low-meat) diet. The outcome was depression. The meta-analysis included twenty longitudinal observational studies. Forest plots were designed, and heterogeneity was analyzed through I² statistic and subgroup analyses. Publication bias was assessed through funnel plots and Egger's test. Results: The pooled overall analysis showed a protective association (HR: 0.74, 95%CI: 0.59-0.89, I² = 53.9%) between meat-free consumption and depression, which was consistent in the group of highest-quality studies. The main sources of heterogeneity identified were study quality, study design, year and country of publication, gender inequality in the country, and adjustment for certain variables (including social variables). The association between flexitarian diet and depression (HR: 0.90, 95%CI: 0.81-0.99, I² = 58.9%) was not consistent between subgroups. Conclusions: The results of this meta-analysis show a consistent protective association between meat-free diets and depression and an inconclusive association regarding flexitarian diet. Primary studies analyzing psychosocial variables are needed to explain these results.