Meta-analysis of 633,317 individuals shows associations between healthy diets and mental health in 23 low- and middle-income countries

There is growing evidence of the association between poor diet quality and common mental disorders, which together contribute to global health syndemics. However, there is no synthesis quantifying associations, assessing robustness of evidence or identifying gaps in Low- and Middle-Income Countries (LMIC) where these concomitant health burdens are most prevalent. We used an Evidence and Gap Map of over 3000 systematically selected, peer-reviewed studies linking food security, diets, and nutrition to anxiety, depression, stress and mental wellbeing (2000-2024). From this, we selected studies investigating associations between healthy diet patterns and mental health symptoms measured by validated tools. Eighty-three studies from 23 countries met inclusion criteria (depression n=69; anxiety n=43; stress n=26), reporting statistical measures for 633,317 unique individuals pooled from 65 LMIC sample populations. Healthy diets were associated with less depression, anxiety, and stress. The Standardized Mean Differences (SMD), expressing effect size in standard deviation units, were -0.29 for depression (95% CI -0.35 to -0.23), -0.25 for anxiety (95% CI -0.35 to -0.16), and -0.24 for stress (95% CI -0.33 to -0.14). Results remained robust when restricted to low Risk of Bias studies: depression (SMD = -0.23, CI: -0.31 to -0.16; n=266,831), anxiety (SMD = -0.19, CI: -0.30 to -0.09; n=116,248), and stress (SMD = -0.22, CI: -0.33 to -0.11; n=12,338). Findings were consistent in direction and magnitude across study designs, dietary measurements, diagnostic tools, and country income levels. We found that mental health is better in individuals with healthy diets in LMIC. Methodological limitations (e.g., cross-sectional design) and few studies from low-income countries created evidence gaps. Low-income settings experience disproportionate health vulnerabilities; thus, building on the relationship between diet and mental health can inform actions to improve both.