Control your diet, control your depression?

Depression affects more than 300 million people around the world, or about 4.4% of the population, and is the single largest contributor to global disability. Figure 1 breaks down the numbers by region of the globe. Traditional treatments for depression revolve around a combination of drug and psychological interventions. However, an emerging body of evidence has suggested that nutrition plays an important role in mental health disorders.

Figure 1: Prevalence of depression

Reference: WHO. Depression and other common mental disorders: global health estimates. 2017.

Observational evidence linking specific nutrients to depression is conflicting,^[1] but studies investigating dietary patterns show more consistent results. A meta-analysis of observational studies showed that adherence to a healthy diet characterized by high intakes of fruit, vegetables, fish, and whole grains was associated with significantly lower odds of having depression,^[2] whereas a Western dietary pattern high in refined grains and processed meats approached significance for being associated with increased odds of depression. Similarly, another meta-analysis^[3] showed that adherence to a Mediterranean diet was associated with a reduced risk for depression and the association between diet and depression appears to be particularly pronounced^[4] among less active people.

Unfortunately, observational research cannot establish causality and is prone to confounding. A recent systematic review^[5] identified 17 randomized controlled trials that investigated the impact of dietary change on symptoms of depression in otherwise healthy adults. The studies varied widely in their methodology, and about half reported a statistically significant improvement in depressive symptoms while the remaining did not. However, only one of the studies in this review included participants with diagnosed depression. In many, having a mental health condition was part of the exclusion criteria.

Since the publication of the above review, a single randomized controlled trial^[6] involving participants with clinical depression has been published. This study compared the impact of combining standard care with an individually tailored lifestyle intervention (general exercise and nutrition guidelines based on government recommendations) to standard care alone. There was no significant difference between the groups in depressive symptoms after 12 weeks. However, this study was not designed to investigate the impact of a dietary intervention per se, and no specific nutrition advice was provided to the intervention group. The study under review is a 12-week randomized controlled trial designed to investigate the efficiency of a dietary program for the treatment of depression.

Observational evidence suggests that a healthy dietary pattern like the Mediterranean diet is associated with a reduced risk of depression, but controlled trials investigating the impact of dietary change on depressive symptoms have shown conflicting outcomes. However, only one of these trials involved participants with diagnosed depression. The study under review tested the efficiency of a dietary program for the treatment of depression in participants with clinical depression.