Eating more vegetables, fruits, wholegrains, legumes, fish, lean red meats, olive oil and nuts, led to a significant reduction in depressive symptoms over a three-month period, said investigators.
At the end of the investigation, a third of subjects in the dietary support group met the definitions of depression remission, compared to 8% of subjects in the social support cohort.
"These results were not explained by changes in physical activity or body weight, but were closely related to the extent of dietary change," said Professor Felice Jacka, director of Deakin's Food and Mood Centre at Deakins University in Australia.
"Those who adhered more closely to the dietary program experienced the greatest benefit to their depression symptoms."
The study’s positive implications also included the physical illnesses that were associated with depression, which are both a cause and consequence of the mental disorder.
"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,” said Professor Jacka.
“Moreover, behavioural changes associated with food (cooking/shopping/meal patterns) are an expected outcome of a nutrition intervention, and these changes in activity may also have had a therapeutic benefit,” the study added.
Although a ‘healthy diet’ is open to interpretation according to the country and culture, general consensus suggests diets rich in plant-based foods, such as vegetables, fruits, legumes and whole grains, coupled with lean proteins like fish, are linked to a lower risk for depression.
Nutritional supplements have also shown usefulness in psychiatric disorders although the bulk of research has been limited to animal studies and observational studies in humans.
A 12-week randomised controlled trial was set up to include 31 adults enrolled in the diet intervention group and 25 adults placed in the social support control group.
Here, participants in the social support control group received either social support, which is known to be helpful for people with depression.
The dietary group received support from a clinical dietitian, consisting of information and assistance to improve diet quality.
This included a focus on increasing healthy food consumption while reducing intake of unhealthy food like sweets, refined cereals, fried food, fast-food, processed meats and sugary drinks.
Depression in remission
The results, published in BMC Medicine, showed the dietary intervention group had a greater reduction in depressive symptoms over the study period, compared to those in the social support group.
"We've known for some time that there is a clear association between the quality of people’s diets and their risk for depression," said Professor Jacka.
"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.
The study added that the results were not without caveats including the small sample size, which increased the possibility that the sample used was not representative of a larger population.
In addition, the differential completion rates in each group: 94% versus 73.5% in the dietary and social support groups respectively may have also affected final results.
Source: BMC Medicine
Published online ahead of print: DOI: 10.1186/s12916-017-0791-y
“A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial).”
Authors: Felice Jacka et al.