The study, which took data from almost 46,000 Australians, found that nutrient-boosting and fat-reduction diets had a “small but significant” effect on women. There were no benefits of dietary interventions for depression or anxiety in men, however.
Moreover, when dieting was combined with exercise, a greater improvement in depressive symptoms was experienced.
“Our analysis of the overall evidence shows that adopting a healthier diet can boost peoples’ mood. However, it has no clear effects on anxiety,” said Joseph Firth, a health researcher at Western Sydney University, who led the study in Australia as part of an international team.
The study also found that all diets appeared to have an equal effect on mental health, with weight-loss, fat-reduction and nutrient-improving diets all having similar benefits for depressive symptoms. This suggests highly specific or specialised diets are unnecessary for most people.
“This is actually good news” said Dr Firth; “Just making simple changes in diet is equally beneficial for mental health. In particular, eating more nutrient-dense meals that are high in fibre and vegetables, while cutting back on fast-foods and refined sugars, appears to be sufficient for avoiding the potentially negative psychological effects of a junk food diet.”
The findings demonstrate the potential impact healthier diets could have on mental health across Australia, though more research is needed before policymakers will have sufficient understanding to be able to improve health across the country.
The evidence of a link between diet and nutrition and mental health has been growing rapidly. Poor diet is now a leading cause of early death across the globe, while mental disorders are among the main causes of disability, scientists believe. Yet the exact mechanisms by which diet can influence mental health are not yet fully understood.
"This important study pools information from a group of studies that explored whether changing diet can improve symptoms of depression. Importantly most of the studies were not targeted at people with clinical depression,” said Michael Berk, professor of psychiatry at Deakin University in assessing the study.
“It also suggests that dietary advice could provide additional benefit to people over and above that provided by medication and psychotherapy. Diet could be added to exercise and smoking cessation as strategies to augment usual treatment,” added Prof. Berk.