A new study from researchers at Australia’s Macquarie University is suggesting a causal connection between diet and depression. The results of a randomized controlled trial found dietary improvements lasting just a few weeks can improve overall mood and symptoms of anxiety.

A number of large epidemiological studies have found strong correlations between poor dietary habits and depression. While this observational correlation seems clear, scientists have been divided over whether there is a causal relationship between the two factors – does a bad diet actively make a person depressed or is a bad diet simply a symptom of depression?

The best way scientists can ascertain causality is through randomized controlled trials and, surprisingly, there have been only a few conducted explicitly investigating whether diet interventions affect clinical symptoms of depression. This new trial was small, and relatively short, however, it still offers useful evidence pointing to a possible causal relationship between diet and mood.

The study examined 76 students with moderate to high symptoms of depression. The cohort was randomized into two groups: one continuing normal dietary patterns acting as a control, and a diet change group offered specific intervention instructions, including a hamper of healthy food items. The diet change group followed general Mediterranean-style eating patterns.

The intervention lasted three weeks, with a three-month follow up period. After the three weeks trial, the diet change group displayed improvements across several measures. Depression scores shifted to normal and the diet group reported lower anxiety scores compared to the group continuing normal dietary practices. Three months later only 21 percent of the diet intervention group reported continuing the healthy eating activities, however, all those that did showed consistent improvements in mood.

Of course, one huge limitation with this kind of dietary trial is there is no way to produce a blind control. The healthy diet cohort knew they were eating a healthy diet and this could contribute to a significant placebo effect. Paul Keedwell, a psychiatrist from Cardiff University who did not work on this new study, suggests the results are useful but conclusions are limited when considering how much diet can directly improve mood.

“While the findings are encouraging there is probably a strong placebo effect operating in the healthy diet group,” says Keedwell. “So, while it is important to eat a healthy diet to help maintain good physical and mental health, I doubt that it is more important than timely access to good psychiatric care, physical exercise and emotional support.”

The researchers behind this new trial do recognize these limitations and make no claim that dietary improvements can solely treat moderate to severe depression. However, the researchers do note there are few downsides to these dietary changes and the majority of evidence does suggest, regardless of causal mechanisms, that a healthy diet is related to improvements in mood.

"Modifying diet to reduce processed food intake and increase consumption of fruit, vegetables, fish and olive oil improved depression symptoms in young adults,” the researchers conclude in a statement accompanying the study. “These findings add to a growing literature showing a modest change to diet is a useful adjunct therapy to reduce symptoms of depression."

The new study was published in the journal PLOS One.

Source: PLOS via EurekAlert