There’s a biochemical explanation for why diet may affect brain health, and it comes back to the gut.

“We’re increasingly learning that the health of the gut—so that includes the gut microbiome—is closely linked to the health of our brains,” says Austin Perlmutter, a doctor of internal medicine and senior director of science and clinical innovation at Big Bold Health. The gut microbiome is made up of trillions of microorganisms living in our gastrointestinal tract that interact with the nutrients we digest.

Experts note that messages from the gut, in the form of immune signals, can be sent to the brain through the vagus nerve. Diet can affect those signals, which can be “trained” or “programmed” by our gut and, therefore, what we eat, Perlmutter says.

Diet can cause an imbalance of bacteria in the gut, which is associated with inflammation. Studies show that inflammation can negatively affect mood and lead to anxiety-related mental health problems. Other preliminary studies in animals show that changes in the gut affect brain health, including increasing the risk of Alzheimer’s disease and depression.

“If you think about the fact that you have trillions of bacteria in your gut, that you’re taking in all of these different food molecules, and that your immune system is there, you realize that every day all of the input that goes into your gut is shaping your body,” Perlmutter says. “You can start to appreciate that the foods that you eat, the information coming into your gut, has a direct effect on your brain function.”

While there is no one-size-fits-all diet that can improve mental health, there are some tips you can follow—including which food groups to eat—in order to prioritize your brain health through what you feed your gut.

Overall food diversity

While more research is needed to define what it means to have a “healthy microbiome,” a “diverse microbiome” seems to be the closest fit, says Dr. Richard Day, vice president of medical affairs and clinical development at ADM, a food processing company.

“By consuming a large number of different plant fibers, that gives the building blocks for the emergence of diverse bacterial populations,” Day says.

In a study published in the American Journal of Clinical Nutrition, maintaining a diet in eight main food groups, including vegetables, fruits, seafood, and nuts among others, benefited a person’s overall microbiome and gut health.

Fish

Consuming a diet rich in fish and omega-3 fatty acids was associated with a lower risk for depression, according to a 2016 study published in the Journal of Affective Disorders.

Perlmutter recommends eating small, cold-water fish like salmon, mackerel, anchovies, sardines, and herring (also known as SMASH).

Fish are a big part of the Mediterranean diet, which has been linked to positive mental health outcomes. The diet is a way of eating that focuses on plant-based whole foods, fish, vegetables, and healthy fats.

Foods rich in polyphenols

Polyphenols are micronutrients most commonly found in plants, including leafy greens and colorful fruits, like elderberries and blueberries, and can be a positive for brain health.

“One of the things they do is they act as probiotics, so they can positively influence the microbiome,” Perlmutter says. “When we consume polyphenols, they can kind of suppress the growth of unhealthy bugs.”

Foods rich in fiber

High-fiber foods are also shown to have positive effects on the gut microbiome, which affects the immune system. Consuming fiber produces short-chain fatty acids, which benefit the body in a myriad of ways.

“These short-chain fatty acids can influence our immune system, but it’s also thought that they can get into our brains and influence our brain function,” Perlmutter says. “They may have an anti-inflammatory effect.”

Consider incorporating whole grains, beans, nuts, Jerusalem artichokes, dandelion greens, garlic, and onions into your diet.

“We still need to know a lot more about what types of microbiome interventions may make sense for individuals,” Perlmutter says. “But in an age where hundreds of millions of people have clinical depression, and many more are struggling to improve mood, there is absolutely a pressing need to find new solutions for mood issues, and the gut may offer that.”