Our analysis of the overall evidence shows that adopting a healthier diet can boost peoples’ mood. However, it has no clear effects on anxiety. 

The evidence so far mostly shows that eating healthier reduces mild depression in the general population. Future research should now focus on the effects of dietary interventions in people with clinically-diagnosed psychiatric conditions.

The study also found that all types of dietary improvement appeared to have equal effects on mental health, with weight loss, fat reduction or nutrient-improving diets all having similar benefits for depressive symptoms.
 
This is actually good news. The similar effects from any type of dietary improvement suggests that highly-specific or specialised diets are unnecessary for the average individual.
 
Instead, just making simple changes 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 Australian Bureau of Statistics reports that in 2017-18, 13.1% of Australians had an anxiety-related condition while 10.4% had depression or feelings of depression, and the prevalence for both has increased from 2014-15. At the same time, we know that Australians have room to improve their diets as just 5.4% of adults meet the recommendations for the number daily serves of fruits and vegetables as per the Australian Dietary Guidelines. Fruits and vegetables contain many important nutrients including fibre, vitamins and minerals, as well as phytochemicals like polyphenols, and a variety of these foods should be consumed daily for good health.
 
This study is a meta-analysis which has combined data from a number of independent studies in order to gain greater statistical power and assess whether there is a common effect of diet interventions on mental health outcomes. All 16 included studies of randomised controlled trials reported measures of depressive symptoms, and 11 also reported anxiety outcomes. Notably, only one study comprised a sample which had a primary diagnosis of clinical depression. The analysis showed a significant effect of diet interventions on reducing symptoms of depression compared to control treatment, however there was no overall effect of diet interventions on anxiety outcomes when compared to changes in control groups.  Interestingly, there appeared to be gender differences as consistent positive and larger effects were observed for both depression and anxiety outcomes following diet intervention studies with predominantly (>75%) or all female participants.

Mental health is a growing issue in Australia and this research makes an important contribution to what we know about the effects of diet on mental health outcomes. However, the exact mechanisms by which diet can influence mental health are not yet fully understood. Further investigations are required to identify what diet changes are most beneficial and should be recommended as an adjunct to treatment and part of self-management of mental health symptoms.

ABS source: http://www.abs.gov.au/ausstats/abs@.nsf/mf/4364.0.55.001

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.

The study found improved, although modestly improved, symptoms of depression in people who improved their diet. This confirms previous studies that showed associations between diet quality and depression risk.

Clinical trials are the most robust form of evidence and they provide guidance to clinicians and to people with depression. This suggests that improving diet may make a small yet meaningful contribution to the reduction of depression.

This 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.