A new trial from Deakin University has shown for the first time that improving diet quality can treat major depression.

Director of Deakin's Food and Mood Centre Professor Felice Jacka said the results of her team's new study offered a possible new treatment approach to depression, one of the world's most prevalent and costly medical disorders.

"We've known for some time that there is a clear association between the quality of people's diets and their risk for depression," Professor Jacka said.

"This is the case across countries, cultures and age groups, with healthy diets associated with reduced risk, and unhealthy diets associated with increased risk for depression.

"However, this is the first randomised controlled trial to directly test whether improving diet quality can actually treat clinical depression".

In the study, adults with major depressive disorder were recruited and randomly assigned to receive either social support, which is known to be helpful for people with depression, or support from a clinical dietitian, over a three-month period.

The dietary group received information and assistance to improve the quality of their current diets, with a focus on increasing the consumption of vegetables, fruits, wholegrains, legumes, fish, lean red meats, olive oil and nuts, while reducing their consumption of unhealthy 'extras' foods, such as sweets, refined cereals, fried food, fast-food, processed meats and sugary drinks.

The results of the study, published in the international journal BMC Medicine, showed that participants in the dietary intervention group had a much greater reduction in their depressive symptoms over the three-month period, compared to those in the social support group.

At the end of the trial, a third of those in the dietary support group met criteria for remission of major depression, compared to 8 percent of those in the social support group.

"These results were not explained by changes in physical activity or body weight, but were closely related to the extent of dietary change," Professor Jacka said.

"Those who adhered more closely to the dietary program experienced the greatest benefit to their depression symptoms."

Professor Jacka, who is president of the International Society for Nutritional Psychiatry Research, said the findings offered an important new strategy for the treatment of depression.

"Mental disorders account for the leading cause of disability worldwide, with depression accounting for the large proportion of that burden," she said.

"While approximately half of sufferers are helped by currently available medical and psychological therapies, new treatment options for depression are urgently needed.

"Importantly, depression also increases the risk of and, in turn, is also increased by common physical illnesses such as obesity, type 2 diabetes and heart disease. Successfully improving the quality of patients' diets would also benefit these illnesses."

The study suggests the new possibility of adding clinical dieticians to mental health care teams and making dietitian support available to those experiencing depression.

"It also supports the previous extensive research from human population studies and animal research suggesting that diet is a key determinant of mental and brain health," Professor Jacka said.

Article: A randomised controlled trial of dietary improvement for adults with major depression (the 'SMILES' trial), Felice N. JackaEmail author, Adrienne O'Neil, Rachelle Opie, Catherine Itsiopoulos, Sue Cotton, Mohammedreza Mohebbi, David Castle, Sarah Dash, Cathrine Mihalopoulos, Mary Lou Chatterton, Laima Brazionis, Olivia M. Dean, Allison M. Hodge and Michael Berk, BMC Medicine, doi: 10.1186/s12916-017-0791-y, published 30 January 2017.