Young woman exercising and resting and drinking energy drink outdoors on sunny summer day in training outfit

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The human gut is host to a vast population of microbes. These organ dwellers are constantly changing with our health. Some microbes only show up when we are healthy and others only when we are sick. We currently have some understanding of what these microbes are doing in our guts, but little is known about the health implications of these belly-lodging microbes.

Now, researchers have found a family of microbes that are linked to better exercise performance. These microbes bloom in athletes who work out intensely, like marathon runners and Olympic rowers. When transplanted from athletes to mice, these microbes make the animals run longer. This work identifies a natural, microbe-made process that boosts athletic performance in humans.

Microbe star-studded stomachs

Microbes are everywhere, and the human body is no exception. Some estimates show that there are more microbes in and on each of us than human cells. And these microbes are hardly dangerous to us. If truth be told, our inhabiting microbes play a vital role in keeping us healthy.

Nowhere is this more apparent than in our digestive systems. The gut is home to hundreds of trillions of microbes. In fact, there are more microbes in your gut than there are stars in the Milky Way.

Currently, there are over a thousand known types of cataloged microbes in the human gut. And scientists are finding new roles for this growing pool of known gut microbes. For instance, they help us fight off invading microorganisms and maintain our intestinal linings. They help produce certain vitamins and help us digest certain foods, such as those containing fiber. What’s more, a healthy and balanced microbe population is key to gut health and digestion.

Substances produced by microbes in the gut can even affect other organs. For example, there are gut microbes that communicate with the nervous system. If this signaling goes awry, there can be health consequences involving anxiety and depression.

Marathon-made gut microbes

We carry several pounds of microbes on our skin and in our bodies. These microbes are not the same across individuals. For example, athletes have been found to harbor distinct microbial makeup in the gut. However, what, if any, effects do these microbes have on athletes and, if so, how?

To address this question, scientists looked at some of the world’s elite runners. They gathered samples of feces from 15 first-rate runners for up to a week before and after they ran in the 2015 Boston Marathon. The researchers also took samples from 10 people who did not run on a regular basis (or “non-runners”).

When comparing the samples before and after the race, the researchers found an increase in a family of microbe in runners after the marathon. This microbe belongs to a group called Veillonella. Similarly, the Veillonella in the guts of nearly 100 ultra-marathoners and Olympic trial rowers after working out far outnumbered those of non-runners.

To test if Veillonella produced exercise benefits, the researchers transplanted the Veillonella from marathon runners to the guts of mice. When running to exhaustion on mouse treadmills, most of the mice that received Veillonella ran longer than those mice that did not. Also, the Veillonella-treated mice had less molecules linked to inflammation. This hints that these mice are better protected from injury or stress caused by exercise.

Burning the midnight gastrointestinal oil

When we exercise, our muscles use energy. This energy is processed and used differently depending on the levels of oxygen in our bodies. Under normal oxygen conditions, the body uses oxygen to break down sugars for energy. However, during intense exercises, such as sprinting or a marathon, there may not be enough oxygen available to generate the energy needed to cross the finish line.

When we have little oxygen, muscles begin to produce a molecule called lactate like gangbusters. Normally, sugar (i.e., glucose) is converted to lactate in the muscle, enters the liver via blood circulation, and is then converted back to sugar by the liver. However, lactate can build up in your bloodstream faster than you can burn it off, especially during intense exercise. This results in cramps and exhaustion.

So, what are these Veillonella microbes actually doing? The researchers think that Veillonella microbes are using lactate for energy. And as these microbes feast, they convert lactate into a family of molecules that can enhance exercise performance.

One molecule they found was propionate. This molecule has been shown to reduce food intake and weight gain in humans as well as having positive effects on energy use in fasting humans. Propionate has also been shown to increase the heart rate and maximum rate of oxygen consumption in mice, which would increase exercise performance.

To confirm this, the researchers tested whether Veillonella produces exercise-enhancing molecules like propionate. They took Veillonella taken from athletes and analyzed the molecules the microbes produced. Indeed, the researchers found that Veillonella produced the performance-boosting molecules, including propionate.

A-motional IQ

In the end, the researchers think that the Veillonella microbes process the high levels of lactate in low-oxygen conditions during intense exercise. Then, these microbial byproducts cross into the gut to promote exercise performance. So, the inhabiting microbes of an athlete’s gut are providing an alternative lactate-processing method by converting the building lactate into molecules that reenter the bloodstream to improve athletic performance.

All in all, these naturally occurring microbes in the gut are seemingly recycling an exercise byproduct into an exercise-enhancing molecule. This is an extraordinary example of symbiosis — a close and long-term biological interaction — of humans and microbes, which, in this case, appears to be mutual.

Pro-biotics or con-biotics?

The researchers intend to follow up on this study to find out if the microbes really do help people. Some of them really believe in harnessing the microbiome and are part of the company FitBiomics, which is exploring probiotic supplements. Along these lines, FitBiomics has already filed a patent application for probiotic supplements that could include Veillonella and other exercise-enhancing microbes.

That being said, a lot more research is needed on the transplantation of gut-derived microbes from a healthy individual into a recipient. As of now, the treatment has not been approved by the U.S. Food and Drug Administration (FDA) yet. Earlier this year, the FDA issued a safety alert over the use of gut microbe transplants after one recipient died from the procedure. The FDA says that protections, including screening donors and stool for multi-drug resistant bacteria, are needed before gut microbe transplants become acceptable, let alone commonplace.