Food and Behaviour Research

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

Jacka FN, O'Neil A, Opie R, Itsiopoulos C, Cotton S, Mohebbi M, Castle D, Dash S, Mihalopoulos C, Chatterton ML, Brazionis L, Dean OM, Hodge AM, Berk M (2017) BMC Med.  15(1):23.  doi: 10.1186/s12916-017-0791-y 

Web URL: Read this and related abstracts on PubMed here



The possible therapeutic impact of dietary changes on existing mental illness is largely unknown. Using a randomised controlled trial design, we aimed to investigate the efficacy of a dietary improvement program for the treatment of major depressive episodes.


'SMILES' was a 12-week, parallel-group, single blind, randomised controlled trial of an adjunctive dietary intervention in the treatment of moderate to severe depression. The intervention consisted of seven individual nutritional consulting sessions delivered by a clinical dietician. The control condition comprised a social support protocol to the same visit schedule and length.

Depression symptomatology was the primary endpoint, assessed using the Montgomery-Åsberg Depression Rating Scale (MADRS) at 12 weeks. Secondary outcomes included remission and change of symptoms, mood and anxiety. Analyses utilised a likelihood-based mixed-effects model repeated measures (MMRM) approach. The robustness of estimates was investigated through sensitivity analyses.


We assessed 166 individuals for eligibility, of whom 67 were enrolled (diet intervention, n = 33; control, n = 34). Of these, 55 were utilising some form of therapy: 21 were using psychotherapy and pharmacotherapy combined; 9 were using exclusively psychotherapy; and 25 were using only pharmacotherapy. There were 31 in the diet support group and 25 in the social support control group who had complete data at 12 weeks.

The dietary support group demonstrated significantly greater improvement between baseline and 12 weeks on the MADRS than the social support control group, t(60.7) = 4.38, p < 0.001, Cohen's d = -1.16. Remission, defined as a MADRS score <10, was achieved for 32.3% (n = 10) and 8.0% (n = 2) of the intervention and control groups, respectively (χ 2 (1) = 4.84, p = 0.028); number needed to treat (NNT) based on remission scores was 4.1 (95% CI of NNT 2.3-27.8). A sensitivity analysis, testing departures from the missing at random (MAR) assumption for dropouts, indicated that the impact of the intervention was robust to violations of MAR assumptions.


These results indicate that dietary improvement may provide an efficacious and accessible treatment strategy for the management of this highly prevalent mental disorder, the benefits of which could extend to the management of common co-morbidities.


This pioneering clinical trial found significant benefits for clinical depression from a dietary intervention - hopefully opening the way for more such studies that can increase the range of 'treatment options' available for this very common condition - which often fails to respond to the best standard psychological or pharmacological approaches.

Many previous randomised controlled trials have found that supplementaton with specific nutrients (or micronutrient combinations) can be of benefit in depression - but in most cases, the evidence base is mixed and/or limited.

Intervening to change diet as a whole is a much more 'real-world' intervention - and despite the practical difficulties, this trial has shown that such an approach is not only possible, but likely to prove cost-effective - provided that it can be validated by the replication studies that this trial should hopefully inspire.

Meanwhile, given the limitations of existing treatments for depression, the huge numbers of people affected, and the fact that no side-effects from eating a healthier diet should be expected - other than better health - these findings should also encourage affected individuals and their families, and the professionals who advise them, that dietary changes are an option worth considering.

For a summary of this research, please see the accompanying news article:

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