A randomised controlled trial of dietary improvement for adults with major depression (the 'SMILES' trial).
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 28137247 · doi:10.1186/s12916-017-0791-y
What was done
Sixty-seven adults with moderate to severe major depressive episodes were enrolled in a 12-week, single-blind, parallel-group randomized controlled trial. Participants were randomized to either an adjunctive dietary improvement intervention (n = 33) consisting of seven individual consulting sessions with a clinical dietitian, or an active social support control condition (n = 34) matching the same schedule and session length. Most participants (55 of 67) were concurrently receiving pharmacotherapy, psychotherapy, or both. The primary endpoint was depressive symptom change assessed via the Montgomery-Åsberg Depression Rating Scale (MADRS) at 12 weeks using a mixed-effects model repeated measures approach.
What was found
Complete 12-week data were available for 31 participants in the diet group and 25 in the control group. The dietary support group showed significantly greater improvement on the MADRS compared to the control group (t(60.7) = 4.38, p < 0.001, Cohen's d = -1.16). Remission (MADRS score < 10) was achieved by 32.3% (n = 10) of the diet group versus 8.0% (n = 2) of controls (chi-squared(1) = 4.84, p = 0.028), yielding a number needed to treat of 4.1 (95% CI 2.3–27.8).
Why it matters
This study provides randomized controlled trial evidence that structured dietary intervention delivered by a dietitian can serve as an effective adjunctive treatment to standard care for major depressive episodes.
Limits
The sample size was small (67 enrolled, 56 completed), leading to wide confidence intervals for effect estimates such as the NNT (2.3–27.8). Due to the nature of dietary interventions, participants could not be blinded. The 12-week follow-up does not address long-term maintenance of dietary changes or mood improvements.
Cited by
- supports The SMILES trial was the first randomized controlled trial in depression that demonstrated significant improvements in mood symptoms from a dietary intervention.