Exercise and the Gut Microbiome: 6 Things You Should Know

Good bugs in the gut help motivate you.

Although you should make exercise part of your daily routine, we all have those days when we don’t feel like working out. We make excuses like a stressful day at work, a bad night’s sleep, or bad weather. Believe it or not, recent research shows your gut could be influencing your desire and motivation to exercise.²

Although the study was in mice, the researchers found that microbiome-dependent production of endocannabinoid metabolites (in this case, molecules in the gut produced by bacteria) from Eubacterium rectale and Coprococcus eutactus stimulates sensory neurons and can elevate dopamine levels in the reward-seeking and motivation-networks of the brain – the ventral striatum – during exercise. The researchers concluded that the extra dopamine could boost performance by reinforcing the desire to exercise. 

So, if you are in an exercise-motivational slump, if you can optimize your gut health, then it might power a new outlook on exercise. 

Elite athletes might have an “athletic microbiome.”

Athletes put in hundreds of hours of hard work before game day, focusing on skills, speed, strength, form, and mindset. Some research now suggests that the gut can play a role in performance outcomes, too. 

One small study looked at Boston Marathon runners compared to sedentary controls with the intent to see if there were differences in athletes’ guts that play a role in athleticism.³ The researchers were able to link increases in Veillonella to exercise – because this genus was higher in runners post-marathon compared to non-running controls. Similarly, they saw levels increase in ultra-marathon runners and Olympic trial rowers post-exercise compared to before. 

Although one genus might not sound like a significant finding, the researchers were able to investigate the exact effects of Veillonella in mice studies, sighting interesting and beneficial results to anyone who exercises. Mice with higher Veillonella had 13-percent longer run-to-exhaustion times and less inflammatory cytokines post-exercise compared to control mice. Veillonella species are special in the sense they metabolize lactate into two short-chain fatty acids – acetate and propionate. Propionate has been shown to increase heart rate and VO₂ max, affect blood pressure, improve treadmill performance in mice, and raise resting energy expenditure and fat oxidation in humans when fasting.⁴  

It is unclear if athletes are high performers because of this performance-facilitating organism, or if exercise promotes Veillonella to thrive. Either way, the gut should be considered a critical focus for athletes.

Exercise load matters.

The saying goes: train smarter, not harder. But in the instance of one cycling study, the amount of exercise was shown to have an impact on the microbiome. 

Thirty-three professional and amateur cyclists had their microbiomes analyzed for differences. While there were no major differences reported between cycling status levels, the genus Prevotella was significantly higher in those who reported 16 or more hours of weekly exercise compared to those who exercised only 6-10 hours. Statistically, the study suggests that cyclists who exercise 11 hours or more a week are more likely to have higher Prevotella abundance regardless of whether they were professional or amateur racers.⁵   

Prevotella is a large genus and is generally considered to be a “good” genus of bacteria. Research has found it positively correlates to several amino acid metabolism pathways, including lysine biosynthesis, alanine, aspartate, and glutamate metabolism, carbohydrate metabolism, and the metabolism of vitamins, including vitamin B6, suggesting beneficial support of an athlete’s metabolic pathway.⁵

An athlete’s microbiome can change quickly.

Although most of us – athlete or not – won’t attempt a 100-mile ultra-marathon, this race provides unique physiological conditions to learn how quickly and to what extent extreme exercise changes an athlete’s gut microbiome. 

One elite male trail runner allowed researchers to follow his 21-week training period before the 2019 Western States Endurance Run, famously known for its brutal climbs and descents. Finishing in the top 10 and in less than 16 hours, he provided gut microbiome samples 21- and 2-weeks pre-race, and two hours and 10 days post-race. 

Gut diversity levels decreased during the 19 weeks in between pre-race samples, but increased post-race. Bacteroides (a large genus that includes both ”good” and “bad” species) were relatively unchanged during training pre-race but were reduced by 69 percent just after the race. The relative proportion of the Proteobacteria phylum of bacteria increased by more than fivefold two hours post-race, largely because of a 29-fold increase in Haemophilus (a genus with many significant pathogenic species). This athlete, too, saw increases in Veillonella (up 14,229 percent) and Streptococcus (which, when elevated, can decrease immune readiness) and decreases in Alloprevotella and Subdolingranulum (typically associated with a healthy metabolic status).⁶

Although this study looked at just one individual enduring immense physical exercise, it is still important to understand there can be profound gut microbiome shifts resulting from heavy exercise, but with no noted GI symptoms. It emphasizes the need to start a training season or race weekend with as little dysbiosis as possible to minimize infections known to be associated with prolonged endurance exercise or training under recovery. 

The gut can predict cardiorespiratory fitness.

There are many fitness tests that can be done to estimate a person’s level of cardiorespiratory fitness – the capacity of the circulatory and respiratory systems to supply oxygen to muscle mitochondria for energy production during physical activity. 

Similarly, many athletes train or cross-train their sport with endurance exercises like running, swimming, and cycling to improve fitness. Science reveals telling factors from the gut that correlate with fitness. 

After studying 39 healthy participants with similar age, weight, and diet but different cardiorespiratory fitness levels, researchers found their cardiorespiratory fitness accounted for more than 20 percent of the variation in taxonomic richness. Peak oxygen uptake, the gold standard of cardiorespiratory fitness, played a significant role in microbiomes predicted metagenomic functions, aligning positively with bacterial chemotaxis (how bacteria favorably change in response to environment), motility, and fatty-acid biosynthesis, and showed increases in the production of butyrate, an important and beneficial short-chain fatty acid. They also noted increased abundances of key butyrate-producing taxa (Clostridiales, Roseburia, Lachnospiraceae, and Erysipelotrichaceae) among the fit individuals.⁷

Independent of diet, fitness correlates with increased microbial diversity and production of fecal butyrate among physically fit participants – a key component of the gut for athletes and non-athletes to optimize, because butyrate is also a superstar in overall general health. 

Leaky gut is a risk with exercise load and intensity.

Vigorous exercise redirects blood from the gut to the working muscles to constantly supply oxygen. Couple that with dehydration, high core-body temperatures, hot environmental conditions, frequent training, and long-duration exercise, and the gut can become inflamed, damaged, and weakened, putting the individual at risk for a leaky gut.⁸

However, it is possible to keep the high-intensity, high-volume training, while not falling susceptible to intestinal permeability issues. First, there are barrier-promoting bacterial populations that help maintain integrity. Initial research suggests Lactobacillus plantarum, Bacteroides fragilis, Bifidobacterium longum, and Bifidobacteria bifidum might support intestinal permeability, although more work needs to be done at this species level. Butyrate producers will help integrity, too.⁸ And don’t forget the fiber or non-fiber prebiotics, both of which can improve butyrate levels.

Second, heat tolerance training can help. Hyperthermic conditions will promote intestinal permeability, but research also shows adaptation to chronic heat stress will produce heat-shock proteins, which limit cellular damage from stress and facilitate recovery. Some heat-shock proteins are in intestinal cells (as well as in skeletal muscle, liver, lungs, and the bloodstream) that can increase tolerance to detrimental lipopolysaccharides (LPS), which are heat-stable endotoxins associated with inflammation.⁸

Third, habitual exercise will help the body adapt and improve blood flow and pressure during exercise, lessening the suddenly reduced blood flow and low oxygen availability to the gut’s endothelial cells. 

And last, antioxidants might help reduce the stress on gut epithelial cells during exercise by supporting reactive oxidative species (ROS) tolerance.     

Pair your exercise training with a gut-support plan. Learn which microbes are present in your microbiome via microbiome testing and follow your plan to optimize your microbiome to support cardiovascular fitness and motivation inside and outside of the gym.