When you share your body with trillions of microscopic guests, the way you treat each other matters.
Your mouth, skin, eyes, urogenital tract, and pretty much every other corner of your body is home to bacteria, viruses, fungi, and other microbes that make up your microbiome. And emerging research strongly suggests your gut microbiome could be a cause of depression, multiple sclerosis, Parkinson’s disease, and other brain disorders.
Most of these organisms, mainly bacteria, live along the intestinal tract, primarily in the colon. The gut microbiome is unique to each person. While we share the overarching categories (phyla) of bacteria—mainly Bacillota and Baceroidota—their proportions differ in each of us, as do the types and proportions of the thousands of individual bacteria species.
And you need them—a healthy gut microbiome helps develop and strengthen the immune, nervous, and skeletal systems; finish off the job of carbohydrate digestion; manufacture certain vitamins; maintain the intestinal tract; and support the body in many other ways. But dysbiosis—having an altered gut microbiome or an unhealthy one (such as with too many “bad” bugs, not enough good ones, or less diversity)—may raise the risk of a host of chronic diseases, such as heart disease, diabetes, gastrointestinal cancers, and neurologic disorders such as Parkinson’s disease and autism.
The Gut-Brain Axis
To understand the influence of gut microbes, picture a communication system between the brain and digestive tract. Along this axis, the brain shoots messages to the gut and vice versa. (If you’ve ever had a stomachache while under stress, for example, this could be why.)
Some messages run along nerves, such as the vagus nerve, which extends from the gut to the brain. Others travel in the bloodstream, which ferries substances such as hormones, neurotransmitters, immune cells, and metabolites (by-products of our own cells or those of our microbes).
“Hundreds of metabolites are produced or modified by gut microbes,” says Elaine Y. Hsiao, PhD, endowed chair and associate professor of biological sciences at UCLA and director of the UCLA Goodman-Luskin Microbiome Center. “Some of these can influence mood, neuroinflammation, and neuronal function.”
Dysbiosis and brain disorders often go hand-in-hand and can be bad news for both the brain and the gut. There are differences—sometimes dramatic ones—in gut microbiomes of people with and without neurologic disorders. Scientists hypothesize that dysbiosis might even cause or accelerate brain disorders, too. Years before they are diagnosed with Parkinson’s disease or develop motor symptoms, for example, people often experience constipation, a hallmark of the disorder.
It works the other way around as well.
“A neurologic disorder itself—and even the medications that treat it—can lead to changes in the gut environment that disrupt the microbiome,” says Jaeyun Sung, PhD, a computational researcher and associate professor of biomedical informatics at Mayo Clinic in Rochester, MN. “For instance, Parkinson’s disease often comes with slowed gut motility and constipation, which allows different bacteria to flourish. In reality, it can become a feedback loop: the disease affects the gut, and a perturbed gut might then further influence the disease.”
Care for Your Microbiome
Your gut microbial population is pretty much set by age 4, but there are ways to tweak it. Here’s how to nurture your gut microbiome:
Eat a healthy diet.
Crowd your plate with plant-based foods—fruit, vegetables, legumes, whole grains, nuts, and seeds—and minimize red meat, sugar, and refined grains. The Mediterranean-style diet, which emphasizes healthy fats and plant-based foods, has been linked to a healthier gut microbiome and benefits such as improved symptoms of depression and, for people with Parkinson’s disease, improved cognition, dyspepsia, and constipation.
Consume enough fiber.
The plant-based foods in a healthy diet should supply a decent amount of fiber, with legumes being a particular standout. While we don’t have the enzymes to break it down, our gut microbes have hundreds of fiber-digesting enzymes that transform it into beneficial short-chain fatty acids. While guidelines recommend 25g of fiber daily for women and 36g for men, people typically get only about half that amount.
“The type of fiber matters: fermentable (soluble) fibers—such as in oats, legumes, apples, and barley—are especially effective at promoting short-chain fatty acid producers, while insoluble fibers—found in whole wheat, wheat and corn bran, nuts, seeds, and fruit and vegetable skins—mainly support bowel regularity,” Dr. Hsiao says. “A variety of fiber types is best.”
Eat fermented foods.
The beneficial bacteria in yogurt, kefir, sauerkraut, and kimchi can survive stomach acid and reach your intestinal tract where they may be helpful, especially if you regularly consume these foods. Check labels for “live, active cultures,” because they aren’t in all fermented foods.
Consider supplements.
When it comes to gut health, the big supplement is probiotics, but to be of any use, they must contain live organisms in adequate amounts with a proven health benefit. Prebiotics, meanwhile, are fuel (usually fiber) for your microbiome and also confer a health benefit. Preliminary research has found that both types of supplements show promise in improving anxiety, depression, stress, sleep, and Alzheimer’s disease.
Some polyphenol-rich extracts, such as berries and green tea, can modulate microbial composition and activity to confer benefits, Dr. Hsiao adds.
“Choices should be individualized and discussed with clinicians,” she says.
Keep moving.
Moderate and high-intensity physical activity is linked to a more diverse, abundant, and resilient gut microbiome.
Discover More
To learn more about research into the gut-brain connection, visit our Nutrition section.
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