Researchers pooled data from 83 studies across 23 low- and middle-income countries — 633,317 people in total. The result: those who ate higher-quality diets showed statistically significantly lower levels of depression, anxiety and stress.
The authors built on a systematic evidence map — a database of more than 3,000 peer-reviewed papers from 2000–2024 linking food security and nutrition with anxiety and depression disorders. From that base they selected 83 studies that used validated symptom-rating scales.
Geography — Asia, Africa, Latin America: 23 countries, mostly low- and middle-income. This matters: most previous meta-analyses on the topic focused on Europe and the United States, and this one closes a serious data gap.
The link between a healthy diet and mental health was directionally consistent across all three outcomes. The effect size is expressed as the standardized mean difference (SMD) — a universal measure that's comparable across different rating scales.
| Outcome | SMD | 95% CI | Number of studies |
|---|---|---|---|
| Depression | −0.29 | −0.35 to −0.23 | 69 |
| Anxiety | −0.25 | −0.35 to −0.16 | 43 |
| Stress | −0.24 | −0.33 to −0.14 | 26 |
💡 What an SMD of ≈ 0.25–0.29 means: a small but statistically robust effect. On Cohen's scale, 0.2 is small, 0.5 is medium and 0.8 is large. So diet isn't a "magic pill" for depression — but it is a meaningful factor among many others.
What's particularly important: the results held when the authors restricted the analysis to low risk-of-bias studies, and when they accounted for different ways of measuring diet, different diagnostic instruments and country income level.
This isn't "eat broccoli and depression goes away." But the direction of the effect is clear: a higher-quality diet is consistently associated with better mental wellbeing. In most of the included studies, a "healthy diet" was understood as:
For the average person, the practical takeaway is simple: if you're going through prolonged stress or anxiety, taking a hard look at your diet is a low-cost, low-risk step that may help, alongside sleep, movement and, when needed, professional support.
⚠ This is a preprint. The article is posted on Research Square and has not yet been peer-reviewed. The final reviewed version may differ — the numbers should be re-checked once the paper is published in a journal.
The authors also lay out the limitations honestly:
The expected next step: more longitudinal and interventional studies, especially in regions where the double burden of malnutrition and mental disorders is highest.
The largest meta-analysis to date on this topic in LMIC countries confirms what WHO and earlier European work already suggested: diet quality and mental health travel together. The effect is small but stable across every subsample. Food policy and personal eating habits aren't only about weight and the heart — they're also about mood, anxiety and resilience to stress.
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