SMILES Study: Depression and Nutrition

There is rarely a single study that definitively establishes new knowledge, but occasionally there are studies that open a window into an important new phenomenon. It is the latter type of study that was published last week in the area of nutrition and adult depression.1 The question this study asked was: In adults with depression who eat a poor diet, does teaching them about nutrition have an impact on their mental health? At the end of the 12-week intervention, the answer was: Yes, and in about 1/3 of those adults, depression symptoms dropped below threshold for diagnosis.

This study, called SMILES (Supporting the Modification of Lifestyle Interventions in Lowered Emotional States), was carried out in Australia over 12 weeks. Participants were randomized to receive either Dietary Support (DS) or Social Support (SS). To participate, they had to meet criteria for having had a Major Depressive Episode. And they also had to report on the Dietary Screening Tool that they had low intake of dietary fiber, lean protein, fruits, and vegetables; as well as a high intake of sweets, processed meats, and salty snacks.

Since everyone has an opinion of what might be the ideal diet, it is important to understand that they did not teach a gluten-free or dairy-free approach, nor Paleo or ketogenic, etc. The diet that was taught to the Dietary Support group followed a whole-foods Mediterranean approach, described as follows:

The primary focus was on increasing diet quality by supporting the consumption of the following 12 key food groups (recommended servings in brackets): whole grains (5–8 servings per day); vegetables (6 per day); fruit (3 per day); legumes (3–4 per week); low-fat and unsweetened dairy foods (2–3 per day); raw and unsalted nuts (1 per day); fish (at least 2 per week); lean red meats (3–4 per week), chicken (2–3 per week); eggs (up to 6 per week); and olive oil (3 tablespoons per day), whilst reducing intake of ‘extras’ foods, such as sweets, refined cereals, fried food, fast food, processed meats and sugary drinks (no more than 3 per week).” 

Each participant randomized to DS received 7 hours of sessions with a dietitian. Those assigned to SS received a similar amount of time in a ‘befriending’ arrangement. There were 31 people who completed DS and 25 who completed SS.

On the primary outcome measure of depression (the MADRS), the DS group improved significantly more than the SS group, with a large effect size. And the changes in depression scores were significantly correlated with changes in diet; in other words, the people who improved their diets the most were the ones who experienced the most improvement in mood.

We are especially appreciative of the evaluation of cost provided in this article (watch for a future blog on the topic of government savings possible from embracing nutritional treatments). The estimated weekly cost of food for their participants prior to the intervention was $138AUS; the cost of the recommended diet for the DS group was only $112AUS.

One of the incidental bits of information in this article indicates the huge potential for clinical applications. They screened 166 referrals in order to find the 67 who were randomized; i.e., 99 were screened out. But what is particularly informative is that only 15 of the 99 excluded were screened out because they had a diet that was ‘too good.’ Or, to express it another way, only 15 out of 166 (9%) of a group of adults with depression met Australian guidelines for having a good diet.

Like any worthwhile study, it raises many other questions: What happened to the 2/3 who did not get much better? Would they have improved if they had been given additional nutrients in pill form? What about people who might have improved more if they had also gone gluten-free? And, importantly, what kind of results would they get if people had not been required to have such a poor quality diet to enter the study?

Finally, we want to conclude by pointing out something that may be obvious, but perhaps not. Finding that improving diet has such a dramatic improvement on 1/3 of people with depression means that poor diet is an extremely important cause of mental disorders.