Diet as a Treatment for Depression: What did we learn from the SMILES Trial?

Diet as a Treatment for Depression: What did we learn from the SMILES Trial?

As a dietitian working directly in psychiatric health care, I am a huge advocate for the role that diet plays in mental health. Part of this advocacy includes staying informed on the latest nutrition and mental health research to support my practice.

I believe food is one of our best means of self-care, and what we put into our body can have a huge impact on how we feel. You are what you eat. Science is quickly catching up to support this familiar rhyme.

Although there have been several studies which have looked at different dietary factors and micronutrients and the role they play in psychiatric conditions such as depression and anxiety, very few studies have looked at the idea of a dietary pattern as the treatment for a mental health disorder.

Enter the SMILES trial… the first of its kind to look at diet as a primary treatment for clinical depression.

What was the SMILES Trial?

The SMILES trial (which stands for Supporting the Modification of lifestyle in Lowered Emotional States), was a randomized clinical trial which took place in Melborne Australia. The study involved 67 adults over the age of 18 who were classified as having “poor diets” and currently experiencing signs of clinical depression.

The study aimed to answer questions like “how does food affect mood and emotions?”, and to see if diet intervention and nutrition counselling could help improve markers of clinical depression.

How it worked

All participants who met the inclusion criteria began with completing a baseline assessment. This involved collecting information on their physical health, lifestyle (activity, smoking, alcohol use, diet), mental health, and social status (education level, occupation, and income).

Participants were randomly assigned to 2 study groups:

1) Control group: The ‘Befriending group’ – Participants met with a member of the research team on a regular basis and discussed subjects they enjoyed but that were not emotional and/or mental health related. 

2) Intervention group: The “Diet group” - Participants received a dietary intervention, which involved meeting with a dietitian for diet education, support and nutrition counselling. Participants in the group were encouraged to follow a modified Mediterranean diet (the “treatment diet”).

Both groups met for a total of 7 sessions over the 12 weeks of the study.

The treatment “diet”

The “prescribed diet” for those in the intervention group was a modification of the mediterranean diet, a diet pattern that emphasizes fresh fruits, vegetables, whole grains, legumes, nuts, extra virgin olive oil, and fish. The diet pattern was coined the “modi-med” diet because it was developed using factors from the Australian and Greek food guide, the traditional Mediterranean diet, and emerging evidence from nutritional psychiatry research.

A visual of the “modi-med” diet is shown here:


Participants in the treatment group received regular support and worked in collaboration with the dietitian to make improvements to their overall diet quality over the length of the study.

The Mediterranean diet

Using the mediterranean diet as a nutrition therapy for health conditions itself is not new; it has been studied for its role in managing chronic conditions such as heart disease, diabetes, blood pressure, and even reducing cancer risk. The emphasis on unsaturated fats from olive oil and nuts and fiber from various plant foods such as produce, nuts, and legumes is thought to be the main driver behind the heart health benefits. These foods are also considered low-glycemic, and as a whole the diet places emphasis on higher fiber carb sources, and lower saturated and processed fats, which may explain the benefit for diabetes and glycemic control. In terms of benefits for the brain and mental health, the emphasis on omega-3 from regular fish consumption (the diet specifies having fish twice a week) may be the main driver.


What were the results?

The results are impressive – published in the journal BMC medicine, they showed that participants in the dietary intervention group had a much greater reduction in their depressive symptoms over the 3-month period compared to 8% of those in the social support group.

At the end of the trial, 1/3 of those in the dietary intervention group met criteria for remission of major depression, compared to 8 % of those in the social support (“befriending”) group.

It was noted by the researchers that the results weren’t explained by changes in physical activity or body weight, but closely related to the extent of dietary change – following the modified Mediterranean diet.

What’s the takeaway?

The SMILES trial provides us with more, high quality evidence to support the role of food in mental health. Dietary strategies offer a low-invasive alternative to medications when it comes to managing a condition like depression as shown by this major study. Depending on the extent of the condition, medications may be required, but I believe it should certainly be encouraged as an adjunctive therapy at the very least.

Further, we already know that the Mediterranean diet has been shown to help manage other conditions like heart disease and diabetes, two chronic conditions that are very common in those with mental health conditions. Did you know that depression is 2-3 times more common in those living with diabetes? Further, heart disease is also linked to depression risk, and the relationship goes both ways. So, the extent of using diet as a treatment for depression, particularly the modified Mediterranean diet, can reach further to support the holistic health of those experiencing the condition.

It also supports the importance of adding clinical dietitians to mental health care. There needs to be more funding to allow for this, and this study offers reasoning to allocate more funding for dietitian presence to support clients with depression in their recovery process.

With depression becoming more prevalent, we need to take a step back and look at how our changing diet in today’s modern society may be playing a role. More emphasis on fast and cheap foods, eating on the go, and losing the connection from our food may be having a negative impact on our health. It is also important to recognize that those living with mental health conditions tend to reside in lower socioeconomic classes, meaning that income may be lower and the risk for food insecurity (aka lack of access to good quality, nutritious food) is higher. However, there needs to be more advocacy work to support the emphasis of diet quality especially in those with limited resources to purchase nutritious food. It may be a tricky battle, but it all starts with awareness.

I hope you enjoyed today’s post and it left you with some food for thought.

Until next time,




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