The SMILES Trial: what’s the real takeaway?
Prior to 2017, dozens of observational and epidemiological studies reported that there may be some kind of relationship between diet quality and one’s mental health. Studies that have yielded a positive association between diet quality and mental health state that the kind of dietary pattern that may improve mental health outcomes includes a pattern that focuses on a whole foods nutrient dense diet inclusive of fruits and vegetables, whole grains, nuts and seeds, fatty fish, and lean meats, and decreased intake of ultra-processed and sugary foods. These observational studies allowed for possible correlations to be determined and until the development of randomized controlled trials, the field was lacking in it’s confidence to say that dietary interventions caused mental health outcomes to improve. Probably the most noted of dietary intervention trials, the SMILES trial, was the first randomized control trial (RCT) conducted in 2017 to assess if a dietary intervention compared to a social or “befriending” group, could produce positive mental health outcomes in a population of adults who were clinically depressed. Here’s their stated hypothesis: “we hypothesised that structured dietary support, focusing on improving diet quality using a modified Mediterranean diet model, would be superior to a social support control condition (befriending) in reducing the severity of depressive symptomatology.”
Method
Participants included in the study were diagnosed with moderate to severe depression via the Diagnostic and Statistical Manual of Mental Disorders (DSM) and screened for poor dietary intake at the time of recruitment. Poor dietary intake was characterized by having a low intake of fruits, vegetables, other plant foods and quality proteins and a high intake of processed or sugary foods. Researchers also used a dietary score to assess compliance to the diet throughout the study. There has been some recent criticism of the specific recruitment strategies since this paper has been published, mostly because of the way they had advertised to seek out their participants. For example, there were advertisements stating: ‘We are trialling the effect of an educational and counselling program focusing on diet that may help improve the symptoms of depression’. If you are curious about the critique, make sure you read this paper. It specifically highlights how expectancy bias is likely a factor with respect to these results which is important to consider when we are thinking about the clinical takeaways of this particular study.
In total, 67 participants were included in the study and were randomly allocated to two groups. The dietary intervention group received personalized dietary recommendations based on a modified Mediterranean diet during 7 60 minute one on one sessions with a clinical dietician. Participants in the social support group received social support via a befriending protocol which consisted of regular meetings to discuss topics of interest or playing games. Here’s a description of the details with regards to both groups: “The dietary intervention comprised personalised dietary advice and nutritional counselling support, including motivational interviewing, goal setting and mindful eating, from a clinical dietician in order to support optimal adherence to the recommended diet.” Both groups met at the same frequency and duration throughout the study. Depression measures were assessed at baseline and at the conclusion of the study using a variety of self report measures including the Montgomery Asburg Depression Rating Scale (MADRS), which was the primary outcome of interest.
Results
After 12 weeks, results indicated that the dietary intervention group showed significantly greater improvements in mental health as compared to the social support group. “The dietary support group demonstrated significantly greater improvement in MADRS scores between baseline and 12 weeks than the social support control group, t(60.7) = 4.38, p < .001 (Fig. 2). The effect size for this difference was a Cohen’s d of –1.16 (95% CI –1.73, –0.59) and represented an estimated average between group difference, in terms of change from baseline to 12 weeks, of 7.1 points on the MADRS (SE = 1.6).” If you are familiar with nutrition research or in psychology, you would know that an effect size of -1.16 is absolutely huge. Typically, an effect size is considered small to moderate (d = 0.2 - .4), medium (d = 0.5 - .07), and large (d = 0.8 and greater) and it’s unusual to see an intervention with that large of an effect size.
It is important to note that beyond getting one on one counseling with a clinical dietician, participants in the dietary intervention group were given hampers of food, incorporating the main components of the diet, along with recipes and meal plans after each dietician session. This significantly increases adherence to the diet when one has the foods available to them in their home along with an understanding of the diet itself and how to cook specific recipes that adhere to the dietary guidelines. Meeting with a clinical dietician for 7 60 minute sessions created a guided individualized support system for the participants who were changing their dietary patterns and habits, something that can significantly increase one’s success with regards to behavior change. These are all independent interventions outside of diet that likely have created these extraordinary results.
Additional Thoughts
They conclude at the end of the study that modifying one’s diet to fit a modified Mediterranean diet, is a useful and effective intervention to help decrease symptoms of depression. In fact, here is what they state in the Discussion section of the paper: In summary, this is the first RCT to explicitly seek to answer the question: If I improve my diet, will my mental health improve? But I want to introduce the major confounding variables that I think, don’t allow us to simply come to the conclusion that diet indeed was the sole factor that caused these significant results. The “structured dietary support” which included meeting with a registered dietician on a regular basis, encouraged participation in a positive adaptive behavior (cooking for oneself). And we know that increasing one’s engagement in positive adaptive behaviors is a very effective behavioral treatment to assist with depression, called Behavioral Activation. It’s effectively, a behavioral strategy that increases a person’s engagement in positive and pleasant activities, thus helping to increase reinforcement, while decreasing punishing behaviors like social isolation, which tends to worsen depression. Behavioral activation independently has really strong effect sizes when we look at this as an independent intervention for depression. This, I would argue, is one of the main interventions used in this study (beyond modifying one’s diet). Meaning, the behavioral intervention within itself (cooking healthy meals for oneself consistently) allows the individual to not only engage in the adaptive behavior of cooking and preparing healthy meals, but it also inherently decreases the person’s engagement in any behavior that may exacerbate or worsen a person’s depression symptoms, simply because the person is now spending time engaged in this adaptive behavior. Additionally, tertiary interventions used like goal setting and motivational interviewing increased the person’s engagement in this goal directed behavior, which are hugely positive when it comes to treating clinical depression.
These are the confounds that exist in this particular intervention study and I think really highlights the need for us to be critical when it comes to interpreting these results. I think the more appropriate question here to ask is: If I improve my diet with the structured guidance and support of a nutrition professional, will my mental health improve?
With regards to the particular takeaways and conclusions we can potentially make from this study, I think it’s crucial to think about these above factors. If anything, the use of personalized sessions with a trained dietician or nutritionist to support dietary changes can be helpful in getting a mild or moderately depressed person to change their diet and that providing resources including handouts of recipes, as well as hampers of foods, increases a depressed person’s ability to adhere to these behavioral instructions.
Is it possible that diet helps to improve symptoms of depression? Maybe. But I think that it’s important to contextualize when diet is able to produce positive mental health outcomes based on the current evidence as well as these important factors of influence. Part of helping us understand this potential relationship, is also looking at other evidence for this relationship in prospective cohort studies. The benefit of the design of these kinds studies is that it allows us to determine over a longer period of time, typically in a healthy population (free of depression), if there is a relationship between one’s diet quality and the risk for developing depression over time. One particular review analyzing results of many prospective cohort studies assessing this relationship, reports that adherenece to a “high-quality diet,” regardless of type (i.e., healthy/prudent or Mediterranean, Tuscan, or vegetarian), was associated with a lower risk of depressive symptoms over time. But what is interesting is that they analyzed the results more comprehensively by accounting for studies that controlled for certain variables at baseline as well as looking at the difference in measures of outcome to see if that made a difference in this potential relationship. They found that studies that controlled for depression severity at baseline or that used a formal diagnosis as outcome did not yield any statistically significant findings. This is critical to understand as this means that a perons’s baseline status regarding depression severity mediates this relationship between diet quality and risk for developing depression long term. It also means that using a formal diagnosis vs. self report measures, are more sensitive to picking up on the diagnostic criteria for depression. Again, these are considerable factors that we need to think about when trying to answer the question if diet is really able to improve depressive symptomology in clinically depressed persons.
