A review of diet study trials finds that positive dietary changes can reduce symptoms of depression, but less of a benefit is seen in addressing symptoms of anxiety.
A healthy diet is a common factor linked to a positive mental outlook. The problem with most of the observational research in this field though is that it is hard to tease out which one comes first.
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?
While observational studies show poor diet is linked to these conditions, intervention studies are needed to really examine the effect that diet can have in improving the outlook of people experiencing these problems.
Fortunately, there is now a growing research interest in seeing how dietary changes can affect mood disorders with depression as the main focus. Depressive disorders affect over 300 million people around the world and are associated with unemployment, poor physical health, impaired social functioning and, in its most severe forms, suicide.
Counselling 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.
With many intervention trials now completed, an Australian research team has gathered the data together into a meta-analysis to look at the overall combined effect that dietary intervention can play on symptoms of depression and anxiety.
Sixteen randomised-controlled trials were included in the analysis, though it should be stated that most of the people in the studies did not meet the criteria for the diagnosis of clinical depression. Even so, dietary intervention was effective in having a small, but meaningful effect in lowering depression symptoms. For anxiety, there was no improvement seen with dietary changes.
There was no one single diet. Many different approaches were used across the interventions. Importantly, there were no differences in depression outcomes between dietary interventions primarily aimed at reducing body weight, improving nutrition or decreasing dietary fat intake. They were all effective.
If dietary change is having a real effect on depression symptoms, then how it could be doing it is still unclear. 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 there.
Then there is growing realisation that gut microbes play an important part in stress responses, immune function and neurotransmission. A switch to more plant-based foods high in fibre is like a fertiliser for the growth of beneficial bacteria. Dietary changes that assist with weight loss can also improve symptoms of depression.
Because most of the studies in the meta-analysis 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 could be an ideal option for people to adopt themselves as a self-management approach for reducing subclinical depressive symptoms.