Smiling women talking in group therapy session
The SMILES trial tested dietary improvement as a treatment for clinically diagnosed depression.

The SMILES trial

The SMILES trial was the first study in the world to demonstrate that making dietary changes can be effective in improving the mental health individuals with clinically diagnosed depression.

Prior to the Supporting the Modification of Lifestyle in Lowered Emotional States (SMILES) trial, a number of studies provided extensive observational evidence that diet quality was directly associated with mental health, particularly depression, across different cultures and life stages.

These studies had shown that higher intakes of fruit, vegetables, whole grains, fish and lower intakes of highly processed and sugary foods were consistently associated with better mental health outcomes.

However, there were no randomised controlled trials to confirm that these relationships were ‘causal’ in nature. Randomised controlled trials are considered the gold-standard in research when establishing causation.

The participants

The SMILES trial tested the efficacy of a dietary program for the treatment of medically diagnosed depression in comparison to social support, which had already been established as helpful for people with depression.

Participants at the time of recruitment into the trial were classified using the the Diagnostic and Statistical Manual of Mental Disorders as having moderate to severe major depressive disorder and poor dietary intake.

Poor dietary intake consisted of a low intake of fruit, vegetables, other plant foods and quality proteins, and a high intake of processed, sugary and salty foods. To assess the quality of the diet, the study used the ModiMedDiet score.

The main outcome of the study was focused on mental health. This was assessed by the Montgomery-Asberg Depression Rating Scale (MADRS).

The trial

Upon enrolment into the trial, 67 participants were randomly allocated into two different groups:

  • Dietary support group (33 participants). Participants in this group received personalised dietary recommendations based on the modified Mediterranean diet – the ModiMedDiet – during regular consultations with a trained dietitian.

  • Social support group (34 participants). Participants in this group received social support according to a ‘befriending’ protocol that included having regular meetings with trained personnel to discuss topics of interest, such as sport or music, and play games together.

Both intervention groups had an equal number of visits of the same duration and intensity. All of the outcomes were assessed at the beginning of the trial (baseline) and at 12 weeks.

The results

After 12 weeks of intervention, the dietary support group showed significantly greater improvements in mental health compared to the social support group.

In the dietary support group, 32% of participants achieved full remission, meaning they were no longer considered depressed.

The people who improved their diets the most also had the most improvement in their depressive symptoms. There was no weight change in either group as this was not a weight loss diet, but rather a diet focused on improving nutritional quality.

Your task

Have you experienced or observed a dietary intervention, or other research in this area in your professional or personal life? Was it successful? What factors contributed to the success or failure of the intervention?

Share your thoughts with other learners in comments.

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This article is from the free online course:

Food and Mood: Improving Mental Health Through Diet and Nutrition

Deakin University