Surprising discovery: Whether we get up to do sports and feel joy about it could also depend on our intestinal flora. Because certain bacteria in the intestine release messenger substances that affect the nerves and brain and promote feelings of happiness during sport, as a study with mice reveals. When researchers killed these bacteria with antibiotics, the previously active animals lost their motivation to exercise. Conversely, a microbe transplant turned them into sports fans.

Exercise is essential for our health: it helps against obesity and depression, keeps the brain fit and can significantly lengthen our lives. But while some people do sport voluntarily after work and are also active at the weekend, this is difficult for many others: Despite good intentions, they always end up on the sofa. But what makes some of us couch potatoes and others sports fans? And why do some people experience a distinct satisfaction from exercising while others hope in vain for a runner’s high?

Lenka Dohnalova from the University of Pennsylvania and her colleagues may have found a new, surprising answer to these questions. For their study, they first gave different breeding strains of mice free access to a running wheel and a treadmill and observed how the individual movement times of the animals differed. In fact, like us humans, there were some mice who used these exercise options very often, while others hardly ever did so.

But why? To find out, the researchers examined the genome, metabolic activity and other parameters of the mice for possible differences between the “sports fans” and those who did not exercise – in total, they recorded more than 10,500 data points per mouse. However, there were no differences either in the genome or in the metabolic activity of the animals that could explain the movement behavior.

Therefore, the team is now investigating another factor: the intestinal flora. Because it has long been known that the bacterial community in our intestines not only shapes our digestion, but can also influence our appetite, our mood and even our mental health. This happens via microbial messenger substances that dock onto the intestinal nerves and thus trigger signals that reach the brain.

Dohnalova and her team initially used a course of antibiotics to investigate whether this gut-brain connection can also influence the desire to exercise. They specifically killed the entire intestinal flora of the “sports fans” among their mice and observed what happened. For the counter-test, the scientists transplanted the intestinal flora of animals that like to exercise into some sedentary mice.

And indeed: The previously motivated and active animals became reluctant to exercise due to the loss of their intestinal flora. Conversely, the transplantation of intestinal bacteria from active mice to “non-sports” mice now turned them into sports fans. More detailed analyzes showed that two types of bacteria were primarily responsible for this: Eubacterium rectale and Coprococcus eutactus. If they were abundant in the intestinal flora, this motivated the mice to exercise.

But how? As the researchers discovered, these intestinal bacteria produce certain molecules called fatty acid amides (FAA). If “lazy” mice were given such fatty acid amides with their food, they too began to move more. Analyzes showed that these bacterial messengers activate a signal cascade that reaches into the brain. Docking to so-called CB1 endocannabinoid receptors in the intestinal nerves triggers a nerve signal that is transmitted to the striatum in the brain. There it causes the release of dopamine – a happy hormone.

This means that the presence of certain microbes in the gut can influence whether exercise triggers a positive mood or even feelings of happiness – similar to the so-called “runner’s high”. In fact, the experiments showed that the mice with an affinity for exercise had a significantly stronger dopamine surge in the brain than their unmotivated conspecifics.

“These results suggest that the intestinal fatty acid amides increase the motivation to exercise in this way,” explain Dohnalova and her colleagues. They suspect that this signaling pathway originally developed to encourage animals to actively search for food and thus to exercise persistently. “This could open up a whole new research direction in exercise physiology,” say the researchers.

According to the scientists, it is obvious that the intestinal bacteria and their metabolic products also have a similar effect on us humans. Accordingly, the composition of the intestinal flora could influence whether we enjoy exercise and sport and are motivated to continue or not. Dohnalova and her team now want to look for such a gut-brain signaling pathway in humans as well.

“If the presence of a similar signaling pathway is confirmed in humans, this could open up an effective way to get people to exercise more and thus lead a healthier lifestyle,” says senior author Christoph Thaiss from the University of Pennsylvania. Because then a targeted diet or the administration of sports-promoting types of bacteria as probiotics could help those who don’t like sports to overcome their reluctance to exercise.

Until then, however, there is still a lot of research to be done, as emphasized by the scientists Gulistan Agirman and Elaine Hsiao from the University of California in Los Angeles, who were not involved in the study, but they also see considerable potential in the new findings: ” If this phenomenon is also relevant for humans, then the psychotropic effects of the microbial molecules would be of great interest for therapeutic options,” they write in an accompanying comment. (Nature, 2022; doi: 10.1038/s41586-022-05525-z)

Quelle: University of Pennsylvania School of Medicine

This article was written by Nadja Podbregar

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The original to this post “The intestines are to blame if you lack the motivation to exercise” comes from scinexx.