Intriguing new research has linked specific gut bacteria to an animal’s drive for exercise by way of a gut-brain route in mice. If the same mechanism is shown to operate in humans, then it may be possible to stimulate a desire to exercise by altering a person’s microbiome.
The study of how physical activity affects the bacteria in the digestive tract is a novel area of microbiome study. Scientists at Harvard Medical School put out an intriguing theory a few years ago: may the bacteria in our stomach affect how well we perform in sports?
After studying the microbiomes of 15 professional marathon runners, the researchers identified interesting alterations to the runners’ microbiomes both before and after a major race. Results from the research raised the possibility that certain types of bacteria are “performance boosting.”
Newer research has probed this concept even further by investigating whether or not the composition of one’s gut flora affects one’s desire to get moving. After having huge amounts of intestinal bacteria eradicated by antibiotics, healthy mice showed a decreased interest in running on a wheel, according to the study.
As a result, a group of researchers at the Perelman School of Medicine began from scratch to explore the potential links between the stomach and exercise motivation. They collected hundreds of mice with varying genetic backgrounds and examined them for any obvious biological variations that would explain the observed variances in their levels of physical activity.
In the first study, researchers looked at how the genomes of various animals varied. Researchers conducted extensive genome-wide associational investigations, but they were unable to identify a single genetic trait that distinguished mice that freely exercised for long periods of time from those who made less of an effort to do so.
However, when they looked at the microbiome, they discovered gut bacteria seemed to be the answer. Antibiotic therapy decreased the rats’ motivation to exercise by around 50%, and the researchers narrowed in on two bacterial species—Eubacterium rectale and Coprococcus eutactus—as likely culprits. However, it was still only a connection. The study’s authors wanted to know whether and how certain bacteria may be impacting subjects’ desire to exercise.
Close examination of the brains of mice revealed that physical activity activated a dopamine signaling route between the intestines and the brain. Exercise seemed to excite sensory neurons in the colon, which in turn sent messages to the brain that resulted in dopamine releases in the striatum, a brain area that regulates movement and reward.
Just exactly was it that was setting off those involuntary reflexes? Two types of bacteria have been related to improved physical performance. Metabolites termed fatty acid amides (FAAs) were produced by both kinds of bacteria and stimulated the gut sensory neurons that sent information to the brain.
The researchers say the evolutionary history of this symbiotic mechanism is among the many intriguing issues addressed by these discoveries. Researchers speculated that a population of gut bacteria that is better adapted to sustained physical exercise may flourish if a restricted number of key nutrients were available in a particular environment. A healthy animal would be one that was intrinsically driven to spend considerable time foraging for a variety of meals.
U.C. Los Angeles biologists provide an alternative explanation in a commentary on the paper, suggesting that the link may have less to do with dopamine-induced physical activity and more to do with pain-signaling activities from the same gut sensory neurons.
It should be noted, however, that these results have only been shown in mice. More research is needed to confirm whether a gut-brain link is present in people.
Important therapeutic strategies may be possible if this is proven in people. More broadly, the researchers suggest that the gut may alter other neurotransmitters and dopamine-dependent pathways, lending credence to the idea that dietary, lifestyle, or metabolite supplementation may help a person’s incentive to exercise. This suggests the microbiome may have a role in the development of several mental disorders.
