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The world’s foremost athletes owe their peak performance to both good genes and tremendous hard work — but that’s not all. According to a new study, microbes that are only found in the guts of athletes may enhance endurance, helping them perform better than regular people who live a sedentary lifestyle.

The findings were reported by researchers at Harvard University who initially analyzed stool samples from 15 competitors in the 2015 Boston Marathon. At the time, the researchers found high levels of a microbe called Veillonella, which spiked after an intense workout and skyrocketed after the marathon. This bacteria is known for breaking down lactate — a byproduct constantly produced in the body during normal metabolism and exercise. It’s what causes aching legs in runners during the last portion of a long race.

A side effect of high lactate levels is an increase in the acidity of the muscle cells, along with disruptions of other metabolites. The same metabolic pathways that permit the breakdown of glucose to energy perform poorly in this acidic environment. It might seem odd that working muscles would produce a substance that would slow their capacity for more work. However, there’s a good reason: lactate accumulation prevents permanent damage during extreme exertion by slowing down biological systems that are required for muscle contraction.

Veillonella absorbs lactate, converting the metabolite into a fuel called propionate. This short-chained fatty acid also has anti-inflammatory properties.

The Harvard researchers later confirmed these findings in another study involving 87 other athletes. Then, in an experiment involving only mice, the researchers colonized a strain of Veillonella collected from one of the athletes. The rodents which had the bacteria in their guts could run 13% longer on treadmills — a huge performance boost in the ultra-competitive world of elite sports where races can be won or lost due to a split-second difference.

The findings support the idea that lactate metabolism is an important component of extreme athlete performance. Previously, other studies had also shown that the microbiomes of athletes differ from those of sedentary individuals.

“Taken together, these studies reveal that V. atypica improves run time via its metabolic conversion of exercise-induced lactate into propionate, thereby identifying a natural, microbiome-encoded enzymatic process that enhances athletic performance,” the authors concluded.

In the future, the researchers would like to find out if they can augment endurance performance in humans as they did in mice. They would also like to see whether the endurance boost is due to the propionate’s anti-inflammatory properties. Perhaps one day you’ll be able to buy lab-made probiotics that contain Veillonella and other endurance-enhancing bacteria — that’s already the goal at an American startup called Fitbiomics. There’s also the possibility that the microbiomes of super-athletes might contain bacteria that help prevent diseases like irritable bowel syndrome, which is another compelling avenue of research.

The findings were reported in the journal Nature Medicine.