In cohorts, the highest Mediterranean diet adherence carried a relative risk of 0.67 for new depression
A meta-analysis of 20 longitudinal and 21 cross-sectional studies: Mediterranean diet, highest against lowest adherence, "relative risk estimate... of 0.67 (95% CI 0.55-0.82)"; a less inflammatory diet, 0.76. Associations, not trials.
Reasonable evidence with real limitations. how we score evidence
Caveat on this rating: Observational associations, confounded by everything that goes with eating well. The Mediterranean estimate rests on four longitudinal studies. One author discloses industry support from food companies. Two corrections were published and were not read for this row.
This is why diet and depression looks so promising in the newspapers: the observational studies. The randomised trials in this set give a much smaller number, and the gap between the two is the usual shape of nutrition science.
Significant findings
The review searched "up to 31st May 2018 for studies that examined adherence to a healthy diet in relation to depressive symptoms or clinical depression." "A total of 20 longitudinal and 21 cross-sectional studies were included," using measures such as Mediterranean diet adherence, the Healthy Eating Index, DASH and the Dietary Inflammatory Index.
"The most compelling evidence was found for the Mediterranean diet and incident depression, with a combined relative risk estimate of highest vs. lowest adherence category from four longitudinal studies of 0.67 (95% CI 0.55-0.82)."
"A lower Dietary Inflammatory Index was also associated with lower depression incidence in four longitudinal studies (relative risk 0.76; 95% CI: 0.63-0.92)." Other indices pointed the same way, "e.g., relative risk 0.65; 95% CI 0.50-0.84 for HEI/AHEI."
The authors' conclusion: "adhering to a healthy diet, in particular a traditional Mediterranean diet, or avoiding a pro-inflammatory diet appears to confer some protection against depression in observational studies. This provides a reasonable evidence base to assess the role of dietary interventions to prevent depression."
The other direction
People who eat well differ from people who do not in income, education, exercise, smoking, drinking, sleep and a hundred things nobody measured. An observational relative risk of 0.67 is an association between being the kind of person who eats that way and being the kind of person who does not get depressed; it is not the effect of the food. The headline number rests on four longitudinal studies. The authors say so themselves: it is an evidence base "to assess" interventions, which is what the Firth 2019 row does, and the randomised answer is a g of 0.16. One co-author discloses industry support from food companies among other funders, on the record.
What this does not show
It does not show that changing diet prevents or treats depression; only a trial can. It does not compare with any treatment. It does not tell anyone what to eat, and this row does not either.
Worth asking
Which comes first: does a bad diet lower mood, or does low mood make it harder to shop, cook and eat well?
Source
Healthy dietary indices and risk of depressive outcomes: a systematic review and meta-analysis of observational studies — Lassale C, Batty GD, Baghdadli A, Jacka F, Sánchez-Villegas A, Kivimäki M, Akbaraly T (2019)
Reputable peer-reviewed journal
Read the source: https://doi.org/10.1038/s41380-018-0237-8
DOI: 10.1038/s41380-018-0237-8
How this was scored
- Study design
- Systematic review of observational studies
- Funding
- Funding not disclosed
- Published in
- Reputable peer-reviewed journal
- Sample size
- not recorded
- Preregistered
- Yes
- Conflicts disclosed
- Yes
- Independent of proponent
- not recorded
- Retracted
- No
Read the full scoring rubric, including what it can't tell you.
Published September 29, 2026.
Questions
How strong is the evidence behind this?
veisund rates this source "moderate evidence". Reasonable evidence with real limitations. It scores 62 out of 100 on our published rubric. One caveat travels with that badge: Observational associations, confounded by everything that goes with eating well. The Mediterranean estimate rests on four longitudinal studies. One author discloses industry support from food companies. Two corrections were published and were not read for this row. The score is calculated from recorded facts about the source — study design, funding, publication venue, sample size, preregistration — not typed in by an editor.
What is the source for this?
Healthy dietary indices and risk of depressive outcomes: a systematic review and meta-analysis of observational studies — Lassale C, Batty GD, Baghdadli A, Jacka F, Sánchez-Villegas A, Kivimäki M, Akbaraly T (2019). Published in: Reputable peer-reviewed journal. DOI: 10.1038/s41380-018-0237-8. The full source is linked on this page so you can read it yourself.
Who paid for this research, and does that matter?
Study design: Systematic review of observational studies. Funding: Funding not disclosed. Independence from the proponent is not recorded. Industry sponsorship is one of the most reliably measured biases in medicine, which is why funding carries real weight in the score rather than sitting in a footnote.
Is this medical advice?
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.