“We were quite surprised by the findings,” researcher Heather Francis, a lecturer in clinical neuropsychology at Macquarie University in Sydney, Australia, told NPR via email. “I think the next step is to demonstrate the physiological mechanism underlying how diet can improve depression symptoms,” Francis said.
“Highly processed foods increase inflammation,” Francis said. “What’s more, if we don’t consume enough nutrient-dense foods, then this can lead to insufficiencies in nutrients, which also increases inflammation,” she said.
Participants in the healthy diet group consumed 6+ servings of fruits and vegetables per week as compared to the controls. “Those who had a greater increase in fruit and vegetable intake showed the greatest improvement in depression symptoms,” Francis said.
Those in the healthy diet group were instructed to increase consumption of whole grains to a recommended 3 serving a day, 3 daily servings of protein, and 3 servings of fish per week. Unsweetened dairy recommendation was 3 servings per day, nuts and seeds 3 tablespoons per day, 2 tablespoons of olive oil per day, and this group was also advised to use spices such as cinnamon and turmeric.
Using a spectrophotometer participants palms were scanned to detect the degree of yellowness of skin which correlates with the intake carotenoids from consuming fruits and vegetables to help measure food intake. Several research questionnaires were also used to evaluate mental health, including one asking how often participants over the prior week they had experienced symptoms of depression.
“We have a highly consistent and extensive evidence base from around the globe linking healthier diets to reduced depression risk,” says Felice Jacka, a professor of nutritional and epidemiological psychiatry at Deakin University’s Food & Mood Centre in Australia.
The Mediterranean diet was associated with a lower risk of depression in A meta-analysis of 22 previously published studies.
Another study found that diets rich in fruits, vegetables, whole grains, fruit, olive oil,and low fat dairy to be associated with a lower risk of depression as opposed to a higher risk of depression was associated with a diet rich in red meat, refined grains, sweets, and high fat dairy.
Associations between depression and diet are independent of other confounding factors like “education, income, body weight and other health behaviors,” notes Jacka, who’s also the president of the International Society for Nutritional Psychiatry Research who adds “this is true across countries, cultures, and — importantly, age groups.”
“The field is certainly very exciting,” said Jerome Sarris, a professor of integrative mental health at the NICM Health Research Institute at Western Sydney University in Australia.
Most of these studies show an association and can not imply causation as they are not able to prove that changes in diet directly cause the improvements/decline in moods, nor can they rule out a placebo effect as participants were able to tell if they were in the healthy diet group.
“We need further mechanistic studies to understand how diet influences mental and brain health,” notes Jacka.
Research also suggests that in addition to inflammation the gut microbiome can affect brain functioning and mental health; more research is needed to better understand these connections to help develop targeted interventions for those with different mental illnesses.
According to Drew Ramsey, a psychiatrist at Columbia University. “We need to talk to mental health patients about what they eat,” Ramsey says. “When people make efforts to care for themselves and adhere to a belief system they feel is good for them, their mental health is going to improve.”
“Diet is certainly part of the picture, but so are physical activity, good psychological care, medication [when needed] … adequate sleep, adequate exposure to nature and balanced lifestyle,” says Sarris. “My general take-home message is about having an integrative approach.”
