Could Gut Bacteria Impact Your Motivation to Exercise?

In a study of mice, researchers show their microbiomes play a role in how much they run and how quickly they grow fatigued

A mouse runs on a wheel
Gut bacteria, more than genetics, impact mice's motivation to exercise, a recent study suggests. Owen Franken via Getty Images

Microorganisms in the gut, known as the gut microbiome, play an important role in human health. They stimulate the immune system and protect against pathogens. They also impact our sleep, moods and risk for certain diseases, according to the Washington Post’s Gretchen Reynolds.

Now, scientists may be able to add one more thing to that list: The gut microbiome might also affect motivation to exercise, suggests a recent study of mice published in Nature.

“The study shows pretty conclusively that in mice, the desire to exercise is influenced by the microbiome,” Anthony Komaroff, a physician at Harvard University who did not contribute to the study, tells National Geographic’s Sanjay Mishra. It “provides a mechanistic explanation as to how the microbiome could influence the appetite of the animals to exercise.”

Scientists wonder whether humans’ willingness to hit the gym is regulated in a similar way. Mouse studies alone can’t prove that your proclivity for moving or sitting is affected by your microbiome—and people might also be motivated by external factors, such as praise from others—but studying these rodents is a step toward understanding ourselves, scientists say.

This paper isn’t the first to look at exercising mice and their microorganisms. Research published last June in the journal Behavioural Processes found that mice bred specifically to be strong runners ran less when given antibiotics that destroyed their microbiomes, per the Post.

In the more recent study, scientists collected 2.1 million data points on 199 mice, ranging from the rodents’ genetic makeup and gut microbiome composition to their exercise capacity, according to New Scientist’s Grace Wade. The researchers also used antibiotics to either partially or fully remove some of the mice’s microbiomes, per the Scientist’s Katherine Irving.

“It’s an insane amount of data,” Matthew Raymond Olm, a computational microbiologist at Stanford University who did not contribute to the study, tells National Geographic.

After examining all this information, the team found that genetics played only a limited role in the mice’s inclination to exercise. But their gut microbiomes had a greater effect: The mice with diminished microbiomes spent less time exercising on a wheel and grew fatigued more quickly when running on a treadmill. To verify these findings, researchers transplanted microbiomes from mice that were strong runners into other mice, which made them able to exercise more.

The team then looked for why such a connection between exercise and the microbiome might exist. They found that when they inhibited neurons involved in producing dopamine, a neurotransmitter that helps us feel pleasure, it similarly reduced mice’s ambition to exercise. They also tied these neurons to molecules produced by the microbiome. Blocking any part of this path from the microbiome to dopamine release led the mice to exercise less.

“Surprisingly, the motivation for exercise is not brain-intrinsic but is regulated by the gastrointestinal tract,” Christoph Thaiss, a microbiologist at the University of Pennsylvania and a co-author of the study, tells New Scientist.

“This is the most comprehensive study I have ever seen,” Theodore Garland Jr., an evolutionary physiologist at the University of California, Riverside, who did not participate in the recent research but co-authored last June’s paper, tells the Scientist. “[It’s] pulling together lots of different pieces that we knew before in different contexts or in isolation of other parts in a way that hasn’t been done before.”

Now, the researchers want to look at humans to see if the rodent research holds up in ourselves. If so, it could have implications for treating symptoms of various diseases that might be eased with exercise, reports the Scientist.

“There are many differences between mice and human physiology,” Thaiss tells National Geographic. “But we’re embarking on a human study that will answer this question.”

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