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

BACKGROUND: Poor diet quality related to common mental disorders contribute to global health syndemics. However, there is no synthesis quantifying associations specifically in Low- and Middle-Income Countries (LMIC) where these concomitant health burdens are most prevalent. METHODS: We drew on a systematic Evidence and Gap Map (EGM) of > 3,000 records from Medline, CAB Global Health and PsycINFO (2000-2024). We selected LMIC studies quantifying healthy diets (validated dietary indices or factor-analytic methods) against validated screening measures of depression, anxiety, and stress, with a healthy versus unhealthy diet comparator. Effect sizes were standardised as mean differences from Hedges' g and pooled using three-level meta-analysis with robust variance estimation (RVE). Risk of bias was assessed, and sensitivity analyses showed robustness across study designs, dietary measures, and country income strata. RESULTS: Eighty-three eligible studies from 23 countries (depression n = 69; anxiety n = 43; stress n = 26), and 65 LMIC sample populations, reported statistical measures for 633,317 unique individuals. The Standardized Mean Differences (SMD) comparing healthy diets to unhealthy diets 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. Findings were similar in direction and magnitude across study designs, dietary measurements, diagnostic tools, country income levels, and estimates adjusted for socio-economic status. Methodological limitations (e.g., cross-sectional design) and few studies from low-income countries created evidence gaps. CONCLUSIONS: Healthy diets were consistently associated with lower depression, anxiety, and stress symptoms in LMIC. These findings call for integrated dietary and mental health programming in LMIC (and in any setting with disproportionate health vulnerabilities), and for longitudinal and intervention research across diverse low-income settings beyond Iran and China.