Staying Healthy

Do our microbes affect our behavior?

From the doctor

By , Editor in Chief, Harvard Health Letter

illustration showing simplistic renderings of the brain and intestine with arrows in both directions between them, representing the interaction between the brain and digestive systemWe've known for almost 200 years that trillions of microbes live on our skin and deep inside us, particularly in our gut. Until recently, we thought they were just freeloaders using our bodies to get food and shelter, causing us no trouble. However, we now know that the genes of these microbes (our microbiome) make many chemicals that affect our body and may influence our vulnerability to heart disease, diabetes, obesity, depression, anxiety, and several degenerative neurological diseases.

Recent studies suggest the microbes within us may also influence our behavior. A study published online Dec. 14, 2022, by the journal Nature compared mice that began exercising when given a running wheel to mice that didn't. There were no differences in their genes. However, there were differences in their gut microbiomes. In the exercisers, there were more bacteria that produced a certain chemical. Whenever these mice ran, that chemical sent signals from the gut up to the brain and ignited the brain's reward centers: they got a "runner's high," and took every opportunity to run. Because of their different microbiome, the "lazy" mice got no such reward and remained couch potatoes. But when the microbiome of the exercisers was placed inside the lazy mice, they began exercising.

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About the Author

photo of Anthony L. Komaroff, MD

Anthony L. Komaroff, MD, Editor in Chief, Harvard Health Letter

Dr. Anthony L. Komaroff is the Steven P. Simcox/Patrick A. Clifford/James H. Higby Professor of Medicine at Harvard Medical School, senior physician at Brigham and Women’s Hospital in Boston, and editor in chief of the Harvard … See Full Bio
View all posts by Anthony L. Komaroff, MD

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