By Dr Tim Crowe

A healthy diet is a common factor linked to a positive mental outlook. But are people who are experiencing depression or anxiety more likely to eat poorly because of their mood? Or does a poor diet worsen depressive and anxiety symptoms?

Fortunately, to answer these questions there is now a growing research interest in seeing how dietary changes can affect mental health. Depressive disorders affect over 300 million people worldwide and are associated with unemployment, poor physical health, impaired social functioning, and, in its most severe forms, suicide. Counseling and medication gain most of the treatment attention for depression, but the promise of dietary changes in helping to improve the outlook of people with depression is gaining traction.

What the science says

With many research trials now completed, a research team has gathered all the clinical trial data together to look at the combined effect that positive dietary changes can have on mental health. What they found was that healthy diet changes were effective in having a small, but meaningful effect in reducing the symptoms of depression. For anxiety, there was not as much of an improvement seen with dietary changes.

There was no one single diet that stood out as many different approaches were used across the studies. Regardless of what sort of positive diet changes were made though, they all had a similar benefit in improving depression and mood. So, whether it was just eating healthier nutrient-rich foods, losing body weight or eating less fat, they all were effective.

Just how do dietary changes work to improve depression?

Biochemical pathways involving inflammation, oxidative stress, and mitochondrial dysfunction are all known to be disrupted in people with mental disorders, so diet could be having a positive impact here. Then there is a growing understanding of how gut microbes play an important part in stress responses, immune function, and neurotransmission. A switch to more plant-based foods high in fiber is like fertilizer for the growth of beneficial bacteria. Dietary changes that assist with weight loss can also improve symptoms of depression if it means the person has more energy and feels better about themselves.

Most of the studies in the review involved people who were not considered clinically depressed, then the results are more applicable to people with subclinical low mood. Because healthy dietary changes already align with public health dietary guidelines then dietary improvement seems an ideal option for people to adopt themselves as a self-management approach for improving mood and their outlook on life.

Reference: Firth J et al. The effects of dietary improvement on symptoms of depression and anxiety: a meta-analysis of randomized controlled trials. Psychosomatic Medicine 2019;81:265-280