Review of the 2017 SMILES study

Title

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

Authors

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

Published

2017

What they did

The study was advertised in medical waiting rooms, universities, and pharmaacies, at potential referral sources as well as with media interviews and social media advertisements. Participants were eligible if they were adults with a diagnosis of major depression and poor dietary quality (low intake of dietary fibre, lean proteins and fruit and vegetables, and a high intake of sweets, processed meats and salty snacks). 67 people were eligible and they were randomly allocated to either dietary support or social support. Dietary support comprised personalised dietary advice and nutritional counselling support from a clinical dietician. The primary focus was on increasing diet quality by supporting the consumption of the following : whole grains; vegetables; fruit, legumes; low-fat and unsweetened dairy foods; raw and unsalted nuts; fish; lean red meats, chicken; eggs; and olive oil, whilst reducing intake of ‘extras’ foods, such as sweets, refined cereals, fried food, fast-food, processed meats and sugary drinks. Red or white wine consumption beyond 2 standard drinks per day and all other alcohol (e.g. spirits, beer) were included within the ‘extras’ food group. The control group met the same number of times for the same amount of time, but with a trained person to discuss neutral topics of interest to the participant, or potentially engaging in alternate activities such as card or board games.

What they found

The group that got dietary support demonstrated significant improvement in their diet, which was associated with reduced symptoms of their depression, with 10 people demonstrating remission of their depression compared to 2 in the social support group (32.3% v. 8%). There was no association with weight loss as there was no quantity limitation.

Questions raised

It is unclear from this study how improving diet quality effects mood, is it a reduction in the harms caused by reducing the “extras,” an improvement in gut microbiome, an improvement in neurotransmitter substrates? The method of effect is unclear based on this study however the relationship demonstrated in this study is consistent with what has been seen in other observational studies in various different settings, suggesting it is likely a real relationship, even though we do not understand how it works.

Blinding (hiding which group a participant is in from the participant and the researchers) is very difficult in this kind of study, this was not a double blind study as the participants knew what they were receiving, additionally the study was advertised and they knew what they were signing up for. It is possible there was some bias in the participants (dietary intervention might work best in the kind of participant who would sign up for a study). There is documented low motivation in depression, and the patients with enough motivation to sign up for this study may therefore be able to adhere to the dietary changes and see the improvements.

With overall less than 100 participants how broadly can these results be generalised?

What it means

Although questions remain about how diet impacts mood and in what context diet modification is best utilised, improving diet quality is a relatively low risk intervention that has potential for significant improvement in depression symptoms. As a mental health gp I am able to not only focus on the mood disorder but the physical body and ensuring it has the adequate and appropriate fuel to function optimally.

However, sometimes a persons relationship with food can also complicate their mood disorder and can be the source of their distress, if this topic causes distress and you need help now, click here for crisis support services.

If you want to talk with a mental health GP to further explore ways in which dietary modifications may be able to improve your mental health, book an appointment here