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 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 67 participants in this 12-week Australian study were depressed adults 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.

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, 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.” Those in the social support/befriending group had seven one-hour meetings with a trained professional who talked to them about neutral. Anxiety, depression and general mood were assessed at the beginning and end of the study, along with biometric and anthropometric 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 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.

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, this was a small study 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 that demonstrates a direct influence of diet on depression. Depressed people who improved their diet felt better. The upshot is that improving diet in line with general guidelines 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.

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 Medicine, 15, 23. http://doi.org/10.1186/s12916-017-0791-y