Your digestive system hosts billions of microbes, collectively called the microbiota or microbiome.

The mix of microbes in your gut — including the balance between friendly and unfriendly bugs — exerts profound health effects.

Friendly microbes help convert food to energy, make certain essential nutrients, and produce healthful "short-chain" fatty acids after digesting foodborne fructans and resistant starches.

When unfriendly bacteria get the upper hand, that imbalance can promote, trigger, or worsen gut problems ranging from irritable bowel syndrome (IBS) to ulcerative colitis and Crohn’s disease.

Imbalanced microbiomes also promote problems beyond the gut, including inflammation, anxiety, depression, brain fog, diabetes, obesity, chronic pain, heartburn, autoimmune disorders, allergies, cardiovascular disease, kidney disease, and more.

Fermented foods such as yogurt — and certain supplements — provide friendly, “probiotic” bacteria, while beans, onions, garlic, whole grains and other foods provide “prebiotic” fibers that feed friendly bacteria.

It certainly makes sense to eat fermented/cultured foods like yogurt, and evidence concerning the value of probiotic pills — albeit mixed — leans in positive directions (see Food May Make or Break Gut HealthGut-Dwelling Bugs Guide Weight and HealthMicrobes Make Some Folks Fat, and Do Friendly Bugs Fight Fat?).

Exercise also appears to improve gut-microbe profiles. That effect has been proven in rodent studies, and there's evidence of similar effects in people, as we reported in Is Exercise the New Yogurt?. )

Let's review several recent studies whose results support the idea that exercise enhances our health in part by enhancing our gut microbiomes.

Study #1: Finnish trial in women sees better gut microbiota after cycling
Last October, researchers from universities in Finland reported the results of a trial that tested the effects of aerobic endurance exercise on gut microbiota (Munukka E et al. 2018).

The Finnish team recruited 17 overweight, relatively sedentary women for a six-week trial, during which they participated in three stationary-bike exercise sessions per week.

The intensity of the training was controlled by measuring each participant’s heart rate, to ensure safety and comparable levels of exercise for each woman. They were not asked to change any lifestyle factors, including diet, to isolate the effects of exercise.

Before and after the trial, the women’s gut microbes resampled to determine the levels of two major families of microbes:

  • Proteobacteria tend to promote inflammation
  • Akkermansia appear to boost metabolisms and help prevent obesity and diabetes

After six weeks stationary-bike exercise, levels of inflammation-promoting Proteobacteria microbes dropped, while levels of metabolism-quickening Akkermansia microbes rose.

Those results echo the findings of previous studies that found higher levels of Akkermansia microbes in physically active adults.

While the test subjects didn’t experience significant weight loss, the exercise did produce other health benefits.

According to study co-author Satu Pekkala, “We found that phospholipids and cholesterol in VLDL [very low-density lipoproteins] particles decreased in response to exercise. These changes are beneficial for cardiometabolic health ...”.

In addition, levels of proteins linked to inflammation dropped in the participants, particularly in their cardiovascular systems.

Study #2: Chinese study sees beneficial changes in long-distance runners
Long-distance running yields immediate metabolic changes that can potentially impact a person’s gut microbiota (GM) within several hours.

A recently published Chinese trial was designed to see whether and how the GM of runners responded to a half-marathon (13 miles) endurance session (Zhao X et al. 2018).

The authors recruited 20 healthy amateur runners (16 men and 4 women; average age 31 years) who participated in the 2016 Chongqing International Half Marathon. Potential participants were excluded if they’d received antibiotics within the prior year or had been diagnosed with gastrointestinal problems or cardiovascular disease.

Before and after the half-marathon race, the runners provided fecal samples, each volunteer’s body mass index (BMI) was measured, and each volunteer was given the same kind of food.

After the race had been run, levels of 40 microbial metabolites had changed significantly, and the levels of certain microbes were significantly different. And these changes were ones considered generally beneficial.

As the Chinese authors wrote, “Our data indicated that long-distance endurance running can immediately cause striking metabolic changes in the gut environment. These findings highlighted the health-promoting benefits of exercise from the perspective of GM [gut microbiota].”

Study #3: U.S.-Colombian study confirms endurance exercise benefits
Scientists from the United States and Colombia collaborated on a recent study that probed the microbiomes of athletes, to see whether and how they differ from those of less-active people.

The scientists sampled the gut microbiomes of 33 amateur and professional cyclists, and the results seem to confirm that regular, vigorous exercise produces beneficial changes (Petersen LM et al. 2017).

The cyclists showed unusually high levels of bacteria belonging to the genus known as Prevotella — members of which enhance several protein and carbohydrate metabolism pathways — and Prevotella levels rose along with the number of hours that an athlete exercised during an average week.

Prevotella-type bacteria also enhance metabolic pathways that result in production of BCAAs (branched chain amino acids). While the clinical evidence is mixed, some suggests that BCAA supplements may reduce exercise-induced muscle damage and soreness, enhance post-exercise muscle repair, and promote muscle-building.

And, compared with the amateur runners, the professionals (who exercised the most) had higher levels of Methanobrevibacter smithii microbes, which tends to stimulate genes that indirectly enhance energy and carbohydrate metabolism pathways.

Study #4: Early exercise nets long-term benefits
Finally, the authors of a recent evidence review concluded that early-life exercise can improve a child’s gut biome, with that effect persisting through adulthood.

As the review authors noted, research in juvenile rodents shows that — compared with sedentary juvenile rats and adult rats that exercised daily — young rats that exercised daily had the healthiest gut microbiomes.

And those findings appear to extend the humans, as we reported in Gut-Dwelling Bugs Guide Weight and Health.

University of Colorado Boulder researchers found that exercise-induced biome improvements in childhood promote healthier brains and metabolisms over the course of a lifetime.

The co-authors of the evidence review noted that — in addition to maternal and childhood diets — gut biomes strongly affect the direction of child development, and that the gut biome is particularly “plastic” (changeable) from infancy through early childhood.

Senior author Monika Fleshner is a professor in CU-Boulder's Department of Integrative Physiology. As she said, “Exercise affects many aspects of health, both metabolic and mental, and people are only now starting to look at the plasticity of these gut microbes.”


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