Diet tips aren’t something you’d traditionally seek out from a shrink, but some therapists are starting to offer nutritional advice as part of their counseling. The young field of nutritional psychology (or nutritional psychiatry — the terms are used interchangeably) is a new addition to “lifestyle medicine,” a movement that advocates for behavioral changes to play a central role in improving patient health outcomes and managing illness.
The theory behind nutritional psychology is simple: Dietary changes, such as cutting back on processed foods and loading up on seafood for its omega-3 fatty acids, can have a measurable impact on mental health. Yet despite early, intriguing research on the diet-psychology connection, this emerging field lacks important safeguards, such as standardized treatment protocols or formal training requirements — or regulations of any kind. That’s reason enough, experts say, to take a good, skeptical look at anyone who calls themselves a nutritional psychologist before signing up for their take on yesterday’s breakfast.
Diet and mental health: what we know
About a decade ago, an Australian research team found the first hints of a connection between diet and common mental disorders such as depression and anxiety. Previous studies had examined how consuming individual foods or nutrients affects mental health. But Felice Jacka, a professor of nutritional and epidemiological psychiatry at Deakin University in Australia, wanted to see if daily eating habits had a meaningful relationship to mental health. So Jacka and her colleagues tracked diet patterns and symptoms of common mental disorders in a group of more than 1,000 women over a 10-year period. They found a clear link between diet quality and depression.
Jacka’s team uncovered the same link in teenagers and Norwegian adults soon afterwards. Then, in a 2017 clinical trial, they found that participants with major depressive disorder who received personalized dietary advice and nutritional counseling reported significantly reduced depressive symptoms. These study participants had modified their diets by loading up on produce, whole grains, legumes and lean protein, and cutting down on sugary and processed foods. “This showed you could help people with clinical depression to make simple, feasible, inexpensive changes to their diets that had a substantial impact on their symptoms,” says Jacka, who is also president of the International Society for Nutritional Psychiatry Research and director of the Food and Mood Centre in Australia.
Most recently, Jacka’s team performed a meta-analysis of 16 clinical nutrition trials, to see if any associations between healthy eating and mental health bore out across a larger pool of research. Dietary changes reduced depressive symptoms, they found, but appeared to have no measurable effect on anxiety.
Other experts are building on Jacka’s work: A different Australian team ran a follow-up study based on her 2017 trial, and published the results this summer. They found that a Mediterranean diet supplemented with fish oil reduced depression symptoms substantially. At this point, a Mediterranean diet is the only kind whose benefits for depression are supported by research.
Despite repeated evidence of a link between food and mental health, the exact nature of the link remains unclear. Experts believe a few factors may be at play. First, some foods might promote inflammation (the immune system’s response to invaders), which is a risk factor for depression.
Second, “mental health depends on brain health, and brain health depends on food,” says Drew Ramsey, a psychiatrist and professor at Columbia University. “If you’re missing certain nutrients, such as vitamin B12, iron and omega-3 fatty acids, you will get depressed.” Studies also show that dietary changes can affect the size of the hippocampus, the brain region that’s in charge of memory and learning and is most closely associated with psychiatric disorders.
Finally, what we eat affects which types of bacteria live in our guts, which matters because our microbiota might influence our mental health. When scientists transplant fecal matter from humans with schizophrenia or depression into rodents, the animals exhibit behaviors like those of the source humans. Though findings are still inconclusive, other research indicates that probiotics might help those with depression and anxiety.