The connection between food and health is clear, with ever-mounting evidence showing that a healthy diet significantly lowers the risk of everything from heart disease to cancer. And intriguing new research suggests that the benefits of a good diet might go beyond physical health and into mood and mental health as well.
Researchers in the field — known as nutritional psychiatry — are looking into links between diet and anxiety, depression and even psychosis. But the evidence is most robust around depression. The first hints of a link between diet and depression came in the late ’90s, and the field has been growing since then. This past year was a banner year for nutritional psychiatry, as the first two randomized controlled trials on the subject were published.
“We’re at a very exciting time right now with nutrition and mental health, where we have a lot of good evidence to suggest that nutrition, whether that be supplements or diet, can improve symptoms of depression,” says Karen Davison, a registered dietitian who co-led the advisory team on Bridging the Divide, a joint project from the Dietitians of Canada, the Canadian Mental Health Association and Kwantlen Polytechnic University, which highlighted the research in this area last year.Want To Eat Less Meat? These Are The Most Filling Plant Proteins
The first randomized controlled trial, an Australian study called the SMILES trial published last January, assigned 31 people to change their diet, and compared them with 25 who instead received social support, where a trained staffer befriended the person and either discussed topics they were interested in or did an activity with them they enjoyed, like playing card games. It found that 32 percent of those who changed their diets went into remission from their depression, while only 8 percent of those in the control group did. “It was a pretty incredible result,” says Sarah Dash, one of the authors of the paper and a research fellow at the Food & Mood Centre at Deakin University in Australia.
The eating pattern participants followed was based on the Mediterranean diet, but it’s not necessary to follow it exactly to potentially see the same benefits, says Dash. As researchers, “we tend to characterize people’s diets either as a more Western diet, or a more traditional diet,” she explains. Any diet that fits a more traditional pattern — with lots of whole foods, plenty of fruits and vegetables, some legumes and fish, moderate amounts of red meat, and less processed food, is likely to contain the same key components as the Mediterranean diet.
Another randomized controlled trial from Australia last year tested encouraging a Mediterranean-style diet — through nutrition education and cooking workshops — combined with offering omega-3 supplements. They used a control group that attended biweekly social events, which included a range of activities from playing games to sharing photos, to control for the fact that the nutrition support group was getting social support from its classes, which might help reduce depression on its own. The study found that the combination was effective in treating depression. The study also looked at the effects of each separately, and found that being on the diet, eating more nuts, or eating more diverse vegetables were all related to lower rates of depression.
It’s worth noting that both studies focused on adding a healthy diet to existing treatment regimens, including medication and therapy, rather than using it as a substitute.
These randomized controlled trials build on more than a decade’s worth of epidemiological research on the subject — where researchers looked for links between diet and depression from large datasets. That work has been largely positive — a 2014 systematic review looked at 21 studies about diet and mood, and found that people who ate more fruit, vegetables, fish, and whole grains were 16 percent less likely to have depression. But whether or not there’s a cause and effect relationship isn’t entirely clear.
When researchers from the University of Ottawa looked at Canadian data from the National Population Health Survey, for example, they found that the strong relationship they saw between fruit and vegetable consumption and depression disappeared once they controlled for smoking and physical activity. “There’s a strong body of evidence showing this association between diet and mental health, but it is very complex,” says Ian Colman, the author of that study and a Canada Research Chair in Mental Health Epidemiology. “There is a fair degree of healthy skepticism [about that relationship], because we know that people who have a healthy diet are more likely to engage in other healthy behaviours.”Subscribe To Our Newsletters — And Kick Your Health Into High Gear
There is also a gap in the evidence around the process by which diet might be affecting mood. There are a few theories: one, that the Mediterranean-style diets being tested are high in healthy fats, like omega 3s, which are thought to be good for your brain. Another idea is that a healthy diet changes the gut microbiome — the microorganisms that live in your digestive tract — and that that might produce chemicals that would affect your brain, or reduce overall inflammation. Yet another thought is that some people might be missing trace nutrients, like folate, and a better diet might provide those and make them feel better. “If we eat a healthy diet, many of us just feel physically better,” says Glenda MacQueen, a professor of psychiatry and vice dean of the Cumming School of Medicine at the University of Calgary. “But that doesn’t mean that you’re changing the underlying circuits in the brain that are disrupted by mental illness.”
Arun Ravindran, a senior scientist and staff psychiatrist at the Centre for Addiction and Mental Health and one of the authors of guidelines around complementary and alternative medicine treatments for depression, says the omega 3 component of the healthy diet has the most evidence behind helping depression.
MacQueen is worried that recommending people try changing their diets without a causal link to better mental health might not be a good idea. “Even if it seems harmless to try diet modification, if people commit to it and they try and they don’t feel better, that can feel like that’s one more piece of evidence that this is not going to ever get better, or there’s nothing they can do about it,” she explains.
On the other hand, people who are motivated to adopt a healthier diet to see if it boosts their mood have more reasons to do so. (Though the experts we spoke to were clear that if you’re depressed, this is an addition to standard treatments, not a replacement for them.)“There’s some evidence now that there’s a good chance this will help improve your mental health,” says Colman. “And the worst case scenario is that you’re going to eat healthier food and it’s going to be good for your body. That’s why this area is such a win-win.”