What is 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 of individuals living with clinically diagnosed depression.

Before the Supporting the Modification of Lifestyle in Lowered Emotional States (SMILES) trial, a number of studies provided evidence that 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 are no prior randomised controlled trials to confirm that these relationships were ‘causal’ in nature. Randomised controlled trials, such a SMILES trial, are considered the gold-standard in research when establishing causation.

The participants

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

The primary outcome of the study was focused on mental health.

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 outcomes 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.