From the fast food whistle-blower Super-Size Me to Fed Up’s investigation of “Big Sugar” and politics, many a documentary has wagged its disapproving finger at the Standard American Diet. These types of documentaries have helped educate the masses about how what we put in our bodies affects everything from our weight to our heart health, but there’s another notable victim of the Western diet they tend to gloss over: our mental health.

A recent study out of the Rush University Medical Center in Chicago and funded by the National Institutes of Aging points to a very real connection between our diets and mental wellbeing, and shows it’s something we ought to be paying more attention to. For the study, the researchers collected data from 964 older adults (who are more likely to struggle with mental health, especially depression) and organized them in different groups based on the type of diet they followed: the DASH (Dietary Approaches to Stop Hypertension) diet, the Mediterranean diet, and the traditional Western diet.

The DASH diet emphasizes eating lots of fruits and vegetables, lean animal proteins, some fat-free or low-fat dairy, and limiting foods high in saturated fats and sugar. Meanwhile, the Mediterranean diet emphasizes fish, whole grains, fruits, vegetables, and healthy unsaturated fats from foods like olive oil, nuts, and seeds. Like the DASH diet, it puts the kibosh on unhealthy fats and sugar. On the flipside, though, the Western diet is typically high in unhealthy fats (like the refined oils found in many packaged foods), red meat, and added sugar, but lacking in fruits and veggies.

Related: 5 Scary Ways Eating Too Much Sugar Can Mess With Your Health

The researchers monitored participants for symptoms of depression throughout a period of six-and-a-half years. They found that those who closely followed the DASH diet were 11 percent less likely to develop depression, while those who stuck to a Western diet were more likely to develop depression.

The study only observes a trend, but the link between our diets and wellbeing it highlights is hard to ignore. Plus, the Rush study isn’t the first of its kind; What’s Good recently covered another study that suggests a healthy diet can help treat depression.

Despite this emerging research, the consideration of diet in mental health treatment—known as ‘nutritional psychiatry’—is still considered a new field of study and remains unexplored by many in the medical community. “People often don’t understand the magnitude of the impact nutrition has on health,” says Dr. Michael Gruttadauria, D.C., D.A.C.A.N., a board-certified chiropractic neurologist with the CIIT Center in New York. “Most doctors don’t even appreciate the connection.”

As for what’s behind that connection, interested experts have a few theories. In a 2015 article published by Harvard Medical School, Eva Selhub, M.D., broke down the relationship between diet and mental health quite simply: It’s all about the gut.

About 95 percent of our serotonin (the neurotransmitter that regulates our mood, sleep, appetite, and pain) is produced in our gut, which suggests that our gut function directly influences our mental and emotional function. A diet high in foods that cause an inflammatory reaction in the gut—such as alcohol, processed sugars, artificial sweeteners, and processed foods high in trans fats, saturated fats, and sodium—can diminish our gut function and interfere with our mental wellbeing, says Caitlin Hoff, health and safety investigator with ConsumerSafety.org. Dairy and wheat, which many people have intolerances or allergies to, may also have this effect.

To minimize inflammation and keep your gut—and mind—healthy, the Harvard School of Public Health recommends avoiding (or at least limiting) refined carbohydrates like white bread, fried foods, soda, processed meats like hot dogs, and margarine. A diet that nourishes our mind and body (much like the DASH and Mediterranean diets) emphasizes whole foods, healthy fats, and lots of plants, which provide inflammation-fighting fiber and nutrients to keep our gut healthy.

“The connection between fiber, our gut microbiota, and the immune system is powerful, almost magical,” says gastroenterologist and gut health expert Dr. Will Bulsiewicz, M.D., M.S.C.I. “Although some may believe that fiber simply enters our mouths and comes out in our stool, recent studies show us that certain types of fiber act as fuel for our gut microbes. We call this type of fiber ‘prebiotic’ because it feeds and nourishes the gut bacteria.” This prebiotic fiber is also converted into short chain fatty acids, which directly help fight inflammation.

Quality, fiber-rich carbs, like lentils, apples, and quinoa also trigger our production of serotonin and tryptophan (which helps produce more serotonin), and can also support our mood and feeling of wellness, adds Becky Kerkenbush, M.S., R.D.-A.P., C.S.G., clinical dietitian with Watertown Regional Medical Center in Wisconsin. It’s no wonder the fruit- and veggie-rich DASH and Mediterranean dieters in the Rush study reported a greater sense of wellbeing.