Emerging research shows that physical exercise changes the composition of microbiota in the gut. A new study focuses on the effects of endurance exercise on these bacteria.

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New research unpacks some of the beneficial effects of exercise on our gut microbiotas.

Two studies published at the end of last year showed that exercise alone, without any dietary changes, is enough to change the composition of gut bacteria.

The experiments, conducted both in mice and humans, found that exercise can boost the production of short-chain fatty acids (SCFAs) that reduce inflammation and keep the gut healthy.

Now, a new study zooms in on the specific effects of endurance exercise training on the composition of gut microbiota.

The first author of the paper is Eveliina Munukka of the Institute of Biomedicine at the University of Turku in Finland. She and her colleagues published their findings in the journal Frontiers in Microbiology.

Satu Pekkala, an Academy of Finland research fellow affiliated with the Faculty of Sport and Health Sciences of the University of Jyväskylä, also in Finland, is the corresponding author of the study.

How endurance exercise affects gut bacteria

Munukka and colleagues created a 6-week program of bicycle endurance training, which involved three sessions per week.

The researchers enrolled 17 women who were overweight in the program. The participants had been sedentary before the study but were otherwise healthy.

The intensity of the endurance training was controlled by checking the participants' heart rate. The women did not change anything else about their lifestyle or diet throughout the study so that the effects of exercise alone would become evident.

Using 16S rRNA sequencing, Munukka and team analyzed the composition and function of the participants' gut microbiota.

Overall, at the end of the program, the researchers found a decrease in so-called proteobacteria — that is, gut bacteria that have the potential of causing inflammation — and an increase in beneficial bacteria called Akkermansia, which have links with a better metabolism.

Previous research has found that Akkermansia bacteria are more prevalent in people who are physically active than in people who are not. Some studies have suggested the bacteria may protect against obesity and diabetes.

"However, more studies are needed to prove that Akkermansia might mediate some of the health benefits of exercise," says Pekkala.

Effects on cardiometabolic health

The researcher goes on to report the additional findings of the study: "We found that phospholipids and cholesterol in VLDL [very low-density lipoprotein] particles decreased in response to exercise."

"These changes are beneficial for cardiometabolic health," Pekkala explains, "because VLDL transports lipids from the liver to peripheral tissues, converts into 'bad' LDL [low-density lipoprotein] cholesterol in the circulation, and thus has detrimental cardiovascular effects."

Additionally, endurance training lowered the activity of the so-called vascular adhesion protein-1, which scientists think has anti-inflammatory effects on the vascular system.

The scientists also examined the changes in the functionality of the genes that encoded the gut bacteria.

"The abundance of the functional genes did not change much, which was perhaps to be expected because the diet did not change during training," Pekkala reports.

"If the training period had been longer, greater effects probably would have been seen."