Donate Deakin

Many aspects of lifestyle, such as keeping active, being a non-smoker and maintaining a balanced diet are important factors in keeping physically and mentally healthy. There have been many studies that have demonstrated that a good quality diet is important to the risk of or prevention of mental disorders. However, the idea of diet as a part of the treatment of mental disorders has not yet been studied. The SMILES (Supporting the Modification of lifestyle in Lowered Emotional States) trial is the first of it’s kind to investigate the questions ‘if I improve my diet, will my mood improve?’ The study commenced in 2012 and recruitment was completed in 2015. The results of this study are now published and can be read HERE. The development of the dietary intervention and feasibility data can be read HERE.

Who participated in the trial?

Participants in the SMILES trial were recruited from the community and reported experiencing depression symptoms. Individuals who were interested in participating in the trial completed a comprehensive screening process. Briefly, this process allowed researchers to ensure that participants were experiencing current depression, did not have any comorbid physical/mental conditions that would inhibit their participation or make it difficult to assess their mood, and that they were able to follow a prescribed diet. Full details of the screening process can be found here.

How did the study work?

Participants who met eligibility criteria were invited to a Baseline Assessment. During this appointment, a research assistant collected a range of information on physical health, lifestyle (physical activity, smoking, alcohol use, diet), mental health, as well as personal details such as education level, occupation, and income. At this time, participants also provided a blood sample that would allow the researchers to investigate their current health. Overall, the baseline assessment provides a detailed snapshot of a participant’s current environment, as well as their physical and mental health. This information serves as a basis of comparison, and allows researchers to compare a participant’s status to before the intervention began.

Intervention and control conditions

Participants were randomly assigned to one of two groups. This process was done electronically, so that the study researchers had no input into what group a participant is placed in. The randomisation process helps us to control for factors that might make the two groups in different in some way. For example, randomisation aims to create two equal groups, so that if you do see a change in one or both of your groups, it’s not because one group had a higher level of education, or was made up of only women.

In this study, the control condition was called ‘the befriending group’. Befriending is a tool used in psychology studies, and it is a ‘neutral’, social support process. Participants in this group met with a member of the research team and discussed subjects they enjoyed, but were not emotional or related to their mental health. A control group aims to keep as many details and experiences of the trial the same as the group who is receiving treatment, and the ‘Befriending group’ met with a researcher the same number of times and for the same amount of time as those in the ‘Diet Group”. This was done so that if there was an effect of the treatment being studied, it is more likely that the treatment was truly effective, and that one group didn’t do better than the other because they spent more time with a clinician.

The second group received a dietary intervention, which involved meeting with  an Accredited Practicing Dietitian for dietary education, support and nutritional counselling.  Participants were encouraged to follow a Modified Mediterranean Diet, which was constructed using existing dietary guidelines from Greece and Australia, traditional Mediterranean diet principles, and scientific evidence from the emerging field of Nutritional Psychiatric Epidemiology.

There is a good body of evidence to suggest that a healthy dietary pattern, such as the Mediterranean diet, promotes brain and mental health, and it is made up of fresh fruits, vegetables, whole grains, legumes, nuts, extra virgin olive oil, and fish. Participants worked in collaboration with the dietitian to make improvements to their overall diet quality. For example, increasing their weekly fish consumption, or swapping the occasional chocolate ice-cream for  natural  yoghurt with walnuts and a drizzle of honey.

After three months, participants attended a Follow Up Appointment where they completed all of the same measures they had completed at Baseline. Once again, participant’s provided a blood sample and were assessed on their physical health, diet and mood. By comparing to Baseline results, the research team can make comparisons on whether the befriending or diet group had greater improvements to their depression symptoms. Lastly, participants were followed up via telephone calls six months after their Baseline appointment to once again assess their diet and mental health.


The results of the study, published in the international journal BMC Medicine, showed that participants in the dietary intervention group had a much greater reduction in their depressive symptoms over the three-month period, compared to those in the social support group.

At the end of the trial, a third of those in the dietary support group met criteria for remission of major depression, compared to 8 percent of those in the social support group.

These results were not explained by changes in physical activity or body weight, but were closely related to the extent of dietary change. In other words, those who improved their diet the most experienced the greatest benefit to their depression.

Why is this study important?

Although many people intuitively understand that diet is important to mental health, it’s important to develop high quality scientific evidence in this area. A randomised controlled trial is considered the ‘gold standard’ of research methods, and it helps researchers begin to understand treatment strategies that may be effective for depression. The results of this trial are  very important in directing future research, as well as informing how we manage or treat some common mental disorders such as depression.

Professor Jacka, who is co-director of the Food and Mood Centre and president of the International Society for Nutritional Psychiatry Research, said the findings offered an important new strategy for the treatment of depression.

“Mental disorders account for the leading cause of disability worldwide, with depression accounting for the large proportion of that burden,” she said.

“While approximately half of sufferers are helped by currently available medical and psychological therapies, new treatment options for depression are urgently needed.

“Importantly, depression also increases the risk of and, in turn, is also increased by common physical illnesses such as obesity, type 2 diabetes and heart disease. Successfully improving the quality of patients’ diets would also benefit these illnesses.”

The study suggests the new possibility of adding clinical dieticians to mental health care teams and making dietitian support available to those experiencing depression.