Dietary strategies may reduce symptoms of depression slightly among adults  

Firth J, Marx W, Dash S, et al. The effects of dietary improvement on symptoms of depression and anxiety: A meta-analysis of randomized controlled trials. Psychosom Med. 2019;81:265-280.

Review question

What are the effects of dietary strategies on symptoms of depression and anxiety in adults?

Background

Globally, approximately one in five people experience a depressive or anxiety disorder each year, while many others experience symptoms of these disorders but do not have a formal diagnosis. These disorders are associated with a low quality of life, poor physical health, and impaired social functioning. Previous systematic reviews have suggested that diet may be associated with the onset of depressive disorders and that dietary strategies may have a beneficial impact on symptoms of depression and anxiety. However, currently more research is needed to determine what impact dietary strategies have on symptoms of depression and anxiety.

How the review was done

This is a systematic review and meta-analysis of 16 randomized controlled trials published between 2000 and 2017, including a total of 45,826 participants.

Key features of the studies:

• Participants were adults who experienced symptoms of depression, anxiety, or both. Some had a clinical diagnosis of depression and/or anxiety, but the vast majority did not. 
• Participants engaged in various dietary strategies—such as counselling/coaching, following a prescribed diet, or attending educational group sessions—focused on one or more of the following: cutting down on fat intake, improving nutrition, and driving weight loss. The length of these dietary programs ranged from 10 days to three years. 
• Researchers measured symptoms of depression and/or anxiety.
• Results were compared to “inactive” or “active” control groups. “Inactive” control group participants maintained their usual dietary habits and “active” control group participants engaged in non-dietary activities such as exercise, social support, or counseling.

What the researchers found

Overall, dietary strategies reduced symptoms of depression by a small amount compared to both active and inactive control groups. A closer look at the data on depressive symptoms also showed that dietary strategies that focused on weight loss and reducing fat intake had a statistically significant positive effect. A positive effect was also observed when a nutrition professional delivered the dietary strategies, and when participants were mostly or entirely female.

Overall, there was no effect on symptoms of anxiety. However, a small positive effect on anxiety symptoms was seen in certain cases, such as dietary strategies that focused on reducing fat intake (only based on two studies), and again studies that included the use of a nutrition professional and those that consisted mostly or entirely of female participants. Most studies included in this review were rated as high quality, however due to the large differences between studies and the small effects, more research is needed to understand how strategies to improve diet may influence mental well-being, which types of strategies are most effective, and for whom.

Conclusion

Strategies to improve diet may have a small positive effect on symptoms of depression in adults. The same benefits were not reported for anxiety, except in specific instances. At this point more research is needed to better understand the relationship between dietary strategies and symptoms of depressions and anxiety.