A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial)

Using a randomised controlled trial design, we aimed to investigate the efficacy of a dietary improvement program for the treatment of major depressive episodes

Felice N. Jacka; Adrienne O’Neil; Rachelle Opie; Catherine Itsiopoulos; Sue Cotton; Mohammedreza Mohebbi; David Castle; Sarah Dash; Cathrine Mihalopoulos; Mary Lou Chatterton; Laima Brazionis; Olivia M. Dean; Allison M. Hodge; Michael Berk


Scholarcy highlights

  • The possible therapeutic impact of dietary changes on existing mental illness is largely unknown
  • There are many versions of a ‘healthful diet’ in different countries and cultures, the available evidence from observational studies suggests that diets higher in plant foods, such as vegetables, fruits, legumes and whole grains, and lean proteins, including fish, are associated with a reduced risk for depression, whilst dietary patterns that include more processed food and sugary products are associated with an increased risk of depression
  • The primary efficacy analysis was based on between-group differences in average change from baseline to 12 weeks for the primary outcome measure; these analyses were conducted using planned comparisons within a restricted maximum likelihood-based mixed-effects model, repeated measures approach
  • There were no significant changes observed in the social support control group for any of the key food groups. These findings were confirmed by analysis of the ModiMedDiet scores: the dietary support group showed significantly greater improvement from baseline to 12 weeks on ModiMedDiet scores than controls, t(55.6) = –4.78, p < 0.001; the differences remained after controlling for sex, education, physical activity, baseline body mass index and baseline ModiMedDiet score
  • Upskilling dieticians to best deliver this program to this patient population may be required. In summary, this is the first randomised controlled trial to explicitly seek to answer the question: If I improve my diet, will my mental health improve? Whilst emphasising the preliminary nature of this study and the imperative for replication in studies with larger sample sizes, the results of our study suggest that dietary improvement guided by a clinical dietician may provide an efficacious treatment strategy for the management of this highly prevalent mental disorder
  • The correlation was only significant in the intervention group; the unstandardised beta coefficient was –0.22, indicating a 2.2 score improvement in MADRS with every 10% increase in dietary adherence
  • Future work in this new field of nutritional psychiatry research should focus on replication, ensuring larger samples and more sophisticated study designs, in order to confirm effects and afford sensitivity analyses to identify predictors of treatment response
  • Clinicians should consider promoting the benefits of dietary improvement and facilitating access to dietetics support for their patients with depression

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