Better mood with healthy food?

Globally, depressive disorders^[1] are ranked as the single largest contributor to health issues. They affect over 300 million people worldwide and are estimated to have increased by almost 20% from 2005 to 2015. The depression statistics for the U.S. are shown in Figure 1. Thus, depressive disorders are a large burden on society (through productivity loss and increased healthcare demands) as well as the individual (through unemployment and poor physical and social health). Anxiety is a close second, affecting over 250 million people worldwide with similar societal and individual burdens. This doesn’t even account for sub-clinical symptoms^[2] of depression or anxiety (clinical reference to symptoms that are clear and can be recognized) which are also highly prevalent and still impede quality of life.

According to a return on investment analysis^[3] regarding treatment of depression and anxiety, the cost of exploring and implementing new treatments is estimated to be offset by the benefits by at least three-fold, with the potential to jump up to almost six times the return when the value of health returns is included in the analysis. However, researchers are far from finding sustainable treatment, as medication doesn’t help everyone^[4], generally shows small effect sizes compared to placebo^[5], and is often accompanied by undesirable side effects^[6]. On the other hand, psychotherapy is not always^[7] effective and can be time consuming^[8]. While novel treatments^[9] are being explored, so are connections between diet and behavior^[10] regarding anxiety and depression^[11]. After all, diet quality has been found to be poorer among^[12] individuals with depression and/or anxiety in a dose-response relationship.

Recently, several meta-analyses^[13][14] have reviewed the literature and demonstrated associations between diet quality and risk for depression, mostly from observational studies. Dietary recommendations^[15] have even been suggested for the prevention of depression. Pro-inflammatory dietary patterns^[16] are associated with a higher incidence of depressive symptoms regardless of mental disorder diagnosis. However, not all available studies^[17] support the association between diet quality and depression risk, and only one systematic review^[18] has evaluated different dietary interventions for depressive symptoms and anxiety, but didn’t quantitatively synthesize the evidence with a meta-analysis.

The authors of the study under review aimed to assess the magnitude of any potential influence of dietary interventions on symptoms of depression and anxiety through the first meta-analysis and systematic review of all randomized controlled trials (RCTs) to date on this issue.

Depression and anxiety are common mental disorders that affect over 500 million people worldwide and pose substantial individual and societal burdens. While standard medication and psychotherapy treatments can be effective, they are often accompanied by undesirable side effects or limited by time constraints and variable efficacy, respectively. Several meta-analyses of observational studies have demonstrated associations between diet quality and risk for depression, but some studies do not support the association and only one systematic review evaluated the association with anxiety. The study under review aims to assess both the efficacy and magnitude of dietary interventions on depression symptoms and anxiety in randomized controlled trials.