Key takeaways
Elite rugby players had more diverse gut bacteria than controls, but they also ate far more protein
Athletes' microbes produce more short-chain fatty acids such as butyrate, which may support gut and metabolic health
Most athlete microbiome studies are small and observational, and probiotic effects are strain-specific and modest
Elite athletes are extraordinary in many ways: huge hearts, high VO2max, large energy needs. Researchers have started looking at their gut microbes too. The findings are intriguing, but before you buy a "performance" probiotic, it helps to know how young and associative this research still is.
The rugby studies: Clarke 2014 and Barton 2018
A group in Cork, Ireland, studied 40 professional rugby union players during a pre-season camp and compared them with healthy men of similar size, split into lower and higher BMI groups.
Clarke et al., 2014 (Gut) found that athletes had a higher diversity of gut micro-organisms, representing 22 distinct phyla. Diversity correlated with protein intake and with creatine kinase, a blood marker of heavy exercise. The authors were careful: exercise seemed to benefit diversity, but the relationship was "complex" and tied to the athletes' dietary extremes.
Barton et al., 2018 (Gut) went back to the same players (40 athletes, 46 controls) and analysed what the microbes were doing. Differences were even larger at the functional level than in which species were present. Athletes had:
- More microbial pathways for amino acid and carbohydrate metabolism.
- Higher faecal levels of the short-chain fatty acids acetate, propionate and butyrate.
Short-chain fatty acids feed colon cells, help maintain the gut barrier and act as signals elsewhere in the body.
Microbes and endurance
The strongest causal evidence comes from animals. Scheiman et al., 2019 found that Veillonella, a bacterium that eats lactate, increased in marathon runners after a race, and that giving it to mice extended their treadmill run time. That story is covered in gut microbiome and VO2max. It is a plausible mechanism, not proof that bacteria make human athletes faster.
The reviews: Mohr et al., 2020
A large narrative review in the Journal of the International Society of Sports Nutrition concluded that exercise, athletic diets and training status are associated with a more "health-associated" gut microbiota: more health-promoting species, greater diversity, more microbial metabolites and better gut barrier function. It also stressed that sport-specific diets and environmental stressors shape the athletic gut alongside training itself.
Summary of the evidence
| Question | What the evidence says | Strength |
|---|---|---|
| Do athletes have more diverse gut bacteria? | Yes, in several studies | Moderate, observational |
| Is it caused by exercise or diet? | Both appear to contribute | Unclear |
| Do microbes affect endurance? | Yes in mice | Weak in humans |
| Do probiotics help performance? | Not shown consistently | Weak |
| Do some probiotics reduce colds or gut symptoms? | Some strains, in some studies | Modest |
What about probiotics?
The ISSN position stand on probiotics (Jäger et al., 2019) is a fair summary. Its main points:
- Benefits are strain- and dose-dependent, so results from one product do not transfer to another.
- In athletes, specific strains can reduce the number, severity and duration of upper respiratory tract infections.
- Intense, prolonged exercise, especially in the heat, can increase gut permeability, and some strains may support gut barrier function.
- Claims about body composition, hormones or lactate need more rigorous human trials.
So probiotics are a possible tool for athletes who get frequent colds or gut trouble during heavy training or travel, not a way to raise VO2max. See our probiotics guide for strains with human data.
Why the evidence is still thin
Most athlete microbiome studies compare a few dozen people at a single time point. Athletes and controls differ in diet, body composition, sleep and stress, so it is hard to know what drives what. Methods also vary between labs, and a "diverse" microbiome is not yet a clinical target. Until larger trials link specific microbial changes to measured performance, treat gut bacteria as an interesting marker, not a training lever.
Why athletes' guts might differ
- Diet. Athletes eat more energy, protein and often carbohydrate and fibre. Protein intake tracked with diversity in the rugby study. Read about protein for athletes.
- Training load. Regular exercise changes gut transit, blood flow and immune signalling. More in exercise and gut health.
- Stress and recovery. Heavy training, poor sleep and travel all affect the gut. See VO2max and sleep.
- Body composition. Lower body fat goes with a different microbial profile.
Practical takeaways for athletes
- Eat a varied, plant-rich diet in training, and adjust fibre around races. See fibre and gut health for endurance athletes.
- Fix gut symptoms first. If you suffer during races, runner's stomach strategies such as gut training work better than chasing microbes.
- Train the engine. Polarised training and VO2max workouts move performance far more than any gut intervention known today.
- Treat probiotics as optional, choose strains tested in people and give them a few weeks.
- Measure what matters with the VO2max calculator and race results.
Ongoing diarrhoea, abdominal pain, blood in your stool or weight loss you cannot explain are medical issues. See a doctor rather than self-treating with supplements.
Frequently asked questions
Do athletes have better gut bacteria?
Athletes tend to have more diverse gut bacteria and more microbial short-chain fatty acids than sedentary people, but diet differs a lot between the groups, so exercise alone cannot take all the credit.
Can the gut microbiome improve athletic performance?
Possibly, but it is not proven in people. Mouse studies show microbes can affect endurance, while human evidence is mostly associative.
Do probiotics help athletes?
Some specific strains may reduce upper respiratory infections or gut symptoms in athletes, according to the International Society of Sports Nutrition, but benefits depend on the strain and dose and are modest.
Should athletes test their microbiome?
Consumer stool tests cannot yet tell you how to train or eat for performance. Spend the money on coaching, food or a lab fitness test instead.
Sources
- Clarke SF, et al. Exercise and associated dietary extremes impact on gut microbial diversity. Gut, 2014.
- Barton W, et al. The microbiome of professional athletes differs from that of more sedentary subjects in composition and particularly at the functional metabolic level. Gut, 2018.
- Mohr AE, et al. The athletic gut microbiota. J Int Soc Sports Nutr, 2020.
- Jäger R, et al. International Society of Sports Nutrition position stand: probiotics. J Int Soc Sports Nutr, 2019.
- Scheiman J, et al. Meta-omics analysis of elite athletes identifies a performance-enhancing microbe that functions via lactate metabolism. Nat Med, 2019.