Aug. 20, 2015 -- What's for dinner? The question is popping up in an unexpected place -- the psychiatrist's office.

More research is finding that a nutritious diet isn't just good for the body; it's great for the brain, too. The knowledge is giving rise to a concept called "nutritional (or food) psychiatry."

"Traditionally, we haven't been trained to ask about food and nutrition," says psychiatrist Drew Ramsey, MD, an assistant clinical professor at Columbia University. "But diet is potentially the most powerful intervention we have. By helping people shape their diets, we can improve their mental health and decrease their risk of psychiatric disorders."

Nearly 1 in 4 Americans have some type of mental illness each year. The CDC says that by 2020, depression will rank as the second leading cause of disability, after heart disease.

It's not just a problem for adults. Half of all long-term mental disorders start by age 14. Today, childhood mental illness affects more than 17 million kids in the U.S.

Recent studies have shown "the risk of depression increases about 80% when you compare teens with the lowest-quality diet, or what we call the Western diet, to those who eat a higher-quality, whole-foods diet. The risk of attention-deficit disorder (ADD) doubles," Ramsey says.