January 4, 2023 – Could your gut health be the explanation behind your motivation – or lack thereof – to exercise?
Researchers on the University of Pennsylvania recently looked into this topic and wanted to search out out why some laboratory mice appear to love their running wheels while others largely ignore them.
First, the researchers used a machine learning algorithm to search for biological features that might explain the differences in mice's activity levels. And what they found surprised them: genetics looked as if it would have little to do with it, but differences in gut flora appeared to be more necessary. A handful of studies backed this up: thriving gut microbiomes were related to optimal muscle function in mice.
In fact, when the researchers gave the mice broad-spectrum antibiotics that killed their gut bacteria, their running performance dropped by half. Without antibiotics, nevertheless, the mice largely returned to their previous performance levels.
The results published within the journal Nature in December suggest that the gut microbiome could help regulate the will for exercise.
If this hypothesis is confirmed in humans, it could help explain why so many Americans (about half) don't get the really useful amount of physical activity. Some may blame an absence of time, energy or interest. But perhaps the explanation lies within the trillions of microbes that live in our gut.
This line of research could also result in microbiome-based methods to get sedentary people off the couch or to optimize athletic performance.
But what influence might your microbiome have in your motivation to exercise? To find the reply, researchers focused on the brain.
The gut-brain connection
After treating the mice with antibiotics, the researchers sequenced RNA within the rodents' striatum (the a part of the brain accountable for motivation). They found that gene expression was reduced within the cells' dopamine receptors – the receptors that release the neurotransmitter dopamine and offer you a sense of accomplishment. In other words, mice treated with antibiotics got fewer dopamine rushes after their run.
“It was only when we started focusing on the brain that we realized that the effect of the microbiome on physical performance is mediated by the central and peripheral nervous systems,” says study writer Christoph Thaiss, PhD, a microbiologist on the University of Pennsylvania. “This realization completely changed the direction of the project.”
To discover exactly how bacteria in the big intestine send signals to the brain, the researchers conducted a series of experiments over several years. They identified two forms of bacteria, Eubacterium rectale And Coprococcus eutaktusThese strains produce compounds called fatty acid amides that interact with endocannabinoid receptors within the gut.
These endocannabinoid receptors signal the brain to decelerate the production of monoamine oxidase, the compound that breaks down dopamine. When there's less of this dopamine-depleting compound within the brain, more dopamine can construct up after an extended run, making the mice feel good and able to get back on the wheel soon.
This gut-brain pathway “may have evolved to link the onset of prolonged physical activity to the nutritional status of the gastrointestinal tract,” Thaiss says. Gut bacteria monitor what's in your colon and tell your brain whether you've had enough food to sustain a workout.
Your colon or intestine is home to trillions of microbes with potentially Hundreds of various bacterial strains. These stresses are determined by the food you eat and the environment you're in.
“The genetic influence on the microbiome is rather small,” says Thaiss, “but lifestyle factors have a strong impact on the composition of the gut microbiome.”
He hopes to develop dietary strategies that encourage the expansion of motivating bacteria, the type that make people need to run a 5-mile race.
What's next?
Next, the researchers need to search out out whether the gut also influences people's motivation. To do that, they're analyzing the gut microbiomes of individuals with various levels of motivation to exercise.
“With enough samples, we might be able to correlate the microbiota species found in exercise-motivated individuals,” says study co-author Dr. Nicholas Betley, a biologist on the university.
Variations within the gut microbiome could help explain the “runner's high” that some people experience during a long-distance run. The research could also help encourage strength training or exercise participation.
“Imagine if a sports team could optimally motivate its athletes to train,” says Betley. The laboratory is studying the results of the microbiome on high-intensity interval training.
The researchers speculate that the signals from the gut to the brain could also influence the body's processes in other ways.
“There are so many ways these signals can alter physiology and affect health,” says Betley. “A new set of studies could well establish a whole new branch of exercise physiology.”