Treating Depression with Diet: The 'SMILES' Trial

Regular readers of this blog or anyone who follows me on Twitter for even half a day will be familiar with some of the research on lifestyle interventions for mental health. While these include sleep, exercise and creative pursuits, one of the ones that I keep coming back to is diet. I have reported on epidemiological studies that show a relationship between a consistently healthy diet and depression in the general population and in women. This research has been correlational, it shows that there is a relationship but, technically, cannot say that what causes what. It could be that depressed people are more likely to eat a poor diet. All that changed recently with the publication of a randomised controlled trial of the use of diet as a treatment of depression; The ‘SMILES’ Trial. The research was led by Professor Felice Jacka, who, if you are interested, I recommend you follow on Twitter for updates and links to similar research.  

The 67 participants in this 12-week Australian study were adults who were depressed at the time and who had a clinically defined poor diet. A poor diet was one that was low in fibre, fruit and vegetables and lean protein, and high in sweets, salty snack foods and processed meats. Some participants were receiving treatment in the form of medication, talking therapy or both.

The participants were randomly assigned to either a nutritional intervention group or a befriending control group. In the intervention group the participants had seven one-hour sessions with a registered nutritionist who provided them with personalised nutritional advice including example recipes and meal plans, and coached them around goal setting and motivation to help them to stick to the nutritional recommendations. They were encouraged to eat (servings in brackets):

  • Whole grains (5–8 servings per day);
  • Vegetables (6 per day);
  • Fruit (3 per day); 
  • Legumes/beans (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).

In addition, participants were encouraged to reduce their intake of “‘extras’ foods, such as sweets, refined cereals, fried food, fast-food, processed meats and sugary drinks (no more than 3 per week). Red or white wine consumption beyond 2 standard drinks per day and all other alcohol (e.g. spirits, beer) were included within the ‘extras’ food group. Individuals were advised to select red wine preferably and only drink with meals.” They were told to eat to their appetites and not worry about trying to lose weight, so it wasn’t a ‘diet’ in the colloquial sense. Those in the social support/befriending group had seven one-hour meetings with a trained professional who talked to them about neutral subjects (i.e. not nutrition, mood or anything that might be considered therapy). Anxiety, depression and general mood were assessed at the beginning and end of the study, along with biological data such as weight, waist circumference, fasting blood glucose and cholesterol.

People in the dietary intervention group were four times more likely to be in remission (not depressed) at the end of 12 weeks than those in the befriending group. They also had reduced severity of anxiety symptoms. There was no change in BMI, blood glucose, cholesterol or physical activity within or between the groups. People were not feeling better because they had lost weight but they were definitely feeling better.

What is also interesting is an analysis called the Number Needed to Treat (NNT). The NNT is a rating of a treatment’s efficacy and describes the number of people that need to be on the treatment in order for one unwanted outcome to be prevented or avoided. So, if a (miracle) drug worked for absolutely everyone then the NNT would be 1. If, for example, a migraine treatment had an NNT of 100 then 100 people would need to be on the treatment to prevent one person having a migraine. The NNT in the SMILES Trial was four. This compares favourably to common antidepressant medication which can vary from 5-16, which is still considered effective particularly in relation to the high global rates of depression. The authors also make the point that that this nutritional intervention would also have positive outcomes for other problems that are commonly associated with depression such as heart disease, type 2 diabetes and obesity.

Crucially, the researchers also looked at the affordability of the diet and found that, on average, people adhering to the diet spent $26 less per week on food and drink than they were at the start of the study.

Of course, we have to bear in mind that this was a small study of people from a particular part of the world and it will both interesting and exciting to see the trial replicated with more participants from different ethnic backgrounds. However, it is also, I think, hugely important. It is the first study (as far as I can see) that demonstrates a direct influence of diet on depression. Depressed people who improved their diet felt better. This trial doesn’t tell us how the diet had this beneficial effect; the results were unrelated to any of the other measurements they took. My guess is that future replications will find a link to systemic inflammation and perhaps to action of the gut microbiome, but time will tell. The upshot is that improving diet in line with general guidelines (no extreme diets) had a significantly positive effect on depression. The benefit of this kind of intervention is that there are no waiting lists or side-effects, and it doesn’t have to be expensive. We eat several times a day and this research shows us that each meal provides us with a valuable opportunity to make a difference to how we feel.

Reference

Jacka, F. N., O’Neil, A., Opie, R., Itsiopoulos, C., Cotton, S., Mohebbi, M., Castle, D., Dash, S., Mihalopoulos, C., Chatterton, M. L., Brazionis, M., Dean, O.M. Hodge, A. M. & Berk, M. (2017). A randomised controlled trial of dietary improvement for adults with major depression (the “SMILES” trial). BMC Medicine15, 23. http://doi.org/10.1186/s12916-017-0791-y