Updated October 19, 2019. | Several recent studies show that a diet rich in whole, plant-based foods like fruits, vegetables, and grains may not only help prevent major depression, but also treat it once it has started.

The SMILES Study

The first study was published in the January 2017 issue of BMC Medicine. Called SMILES (Supporting the Modifica­tion of lifestyle In Lowered Emotional States), the 12-week Australian study looked at diet’s impact on the moods of 67 people living with severe depression.

Some participants in the randomized control were already using antidepressants, psychotherapy, or a mixture of both. It was led by Professor Felice Jacka, director of Deakin University’s Food and Mood Centre.

According to the study, “Of these [67 people], 55 were utilizing some form of therapy: 21 were using psychotherapy and pharmacotherapy combined; 9 were using exclusively psychotherapy, and 25 were using only pharmacotherapy.”

The Results

A clinical dietitian met regularly with 31 of the participants. The remaining 23 joined the social support group. The diet group encouraged patients to eschew fast food, sugary drinks, processed meat, refined grains, and fried food. They were encouraged to eat more whole grains, fruits, vegetables, nuts, beans, and legumes. But, it also allowed lean meat and fish. The results after 12 weeks showed that participants who ate a healthy diet reported happier moods.

“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 in a statement. “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. [This] is the first randomized controlled trial to directly test whether improving diet quality can actually treat clinical depression.”

She added, “These results were not explained by changes in physical activity or body weight, but were closely related to the extent of dietary change. Those who adhered more closely to the dietary program experienced the greatest benefit to their depression symptoms.”

Diet and Depression: Other Causes

While studies show that a plant-based diet may reduce depression, diet isn’t all that affects mental health. Research shows that there are a number of other factors that contribute to mental illness such as genetics, socioeconomic status, race, gender identity, and even alcohol and tobacco consumption.

A recent study in the journal Physiological Reports analyzed the role of high sodium intake plays in mental health. The study took place in an urban low-income neighborhood. Eighty-four teenagers, 50 percent male, 95 percent African American, self-reported on their mental health over the course of 1.5 years. Participants provided regular urine samples to monitor sodium levels. Researchers found that those who regularly ate foods high in sodium experienced higher rates of depression.

A growing body of research shows that eating healthy might not be so easy for everyone. According to the report “Unshared Bounty: How Structural Racism Contributes to the Creation and Persistence of Food Deserts,” 23.5 million people in the U.S. live in low-income neighborhoods more than one mile from a supermarket. “When fast food restaurants are closer than supermarkets to a neighborhood, the neighborhood is more likely to make unhealthy food choices,” it says.

Mental Health and Healthy Diet

Socioeconomic status and lack of access to healthy food can impact not only diet, but also mental health. One study of college students in the Appalachian region found that “Food insecurity and fruit and vegetable intake remained significant predictors of depression in males and in females food insecurity remained a significant predictor of depression.”

It notes previous studies, which focused on older adults, also drew a connection between increased risks for depression and anxiety. However, the field is still new. “Historically, nutrition has been overlooked as a contributor to poor mental health,” it says. “But there is an increasing focus on this relationship, largely due to the central nervous system’s need for key nutrients to maintain optimal function,” the study notes.

The study adds that it may be beneficial to further exam diet’s impact on mental health. It continues that mental health conditions and access to food and healthcare services vary from region to region. A fuller understanding of diet and mental health requires further studies. Additionally, the study failed to address certain foods.

“This study focused on fruits and vegetables because they are considered to be indicative of overall diet quality, and on added sugars because of their evidence of being detrimental to mental health,” it said. “However, this study did not examine meat and saturated fats, which may be detrimental for mental health as well.”

Food, Mood, and Research

The focus on the effects that diet may have on mental health, dubbed “nutritional psychiatry,” is a recent development. In 2013, Professor Jacka co-founded the International Society for Nutritional Psychiatry Research. The group aims to grow the field by taking a multi-disciplinary approach to research. She also founded the Food and Mood Center at Deakin University. It acts as a collaborative research center for studying how diet influences mental health. The American Psychiatric Association has also begun including presentions on nutritional psychiatry at their annual conference.

Similar results linking diet and mental health were found in a second, larger study, where participants experienced a boost in mood that lasted for six months. Another study conducted by researchers at Rush University Medical Center, found that adults were less prone to depression if they included a lot of whole, plant-based foods in their diet and avoided fewer processed and animal-based foods.

A 2012 study published in Nutrition Journal found through a randomized control of 39 omnivores that mood improved with a reduction of meat, fish, and dairy products. The study speculates that a plant-forward diet contains less arachidonic acid, which is high in omnivore diets. Research has shown that a high arachidonic acid intake can “promote changes in brain that can disturb mood.”