Your gut bacteria may influence how motivated you are to exercise

A study conducted in mice suggests certain gut bacteria can regulate motivation to exercise by increasing dopamine levels in the brain during physical activity

By Grace Wade

Motivation to exercise may come from the gut in addition to the brain. A study in mice finds that certain gut bacteria can increase the release of dopamine during physical activity, which helps drive motivation.

Though most of us know that exercise comes with many benefits, how much people exercise varies widely, says Christoph Thaiss at the University of Pennsylvania. He and his colleagues wanted to identify physiological factors that may explain this variation.

They collected data from 106 mice on exercise capacity, genetics, gut microbiome composition and more, and fed it to a machine learning model for analysis. The model found that how often mice exercised was most strongly associated with the makeup of their microbiome.

In a series of experiments that followed, the researchers found that mice with depleted gut microbes spent about half as much time voluntarily running on a wheel as those with intact microbiomes. What’s more, they had reduced dopamine levels in their brains during physical activity, suggesting they found exercise less rewarding. The team then repeated these experiments in mice that had intact microbiomes but lacked neurons connecting the gut to the brain and found this resulted in the same effects seen in mice with depleted microbiomes. Together, these findings show the gut plays an integral role in motivation for exercise, Thaiss says.

The team also identified molecules produced by certain gut bacteria called fatty acid amides that, when given to mice with depleted microbiomes, restored how often they exercised to levels seen in mice with intact microbiomes. “Surprisingly, the motivation for exercise is not brain-intrinsic but is regulated by the gastrointestinal tract,” says Thaiss.

This isn’t the first time the microbiome has been found to play a role in functions outside our gastrointestinal system. In fact, previous studies have shown that the bacteria in our guts may influence our mood, control blood sugar levels and even protect against inflammation linked to conditions like heart disease and dementia.

However, it is too early to know if these findings in mice are also true for humans, Thaiss says. He and his team are currently conducting a similar trial in people to see whether we have the same gut-to-brain pathway, and if so, whether leveraging it will boost our motivation to exercise.

Journal reference: Nature, DOI: 10.1038/s41586-022-05525-z