How your gut microbiome affects sports performance

Around 100 trillion microorganisms live in your gut. That is more than the number of cells in your body. This ecosystem is called the microbiome, and it affects far more than your digestion.

Current multi-omics research (2024–2026) shows a two-way relationship between training and the microbiome. Endurance training changes the microbial mix, while microbial metabolites called short-chain fatty acids (SCFAs) influence energy metabolism, immunity and recovery.

For you as an athlete, this means your gut is no passive digestive tube. It is an active training partner that helps decide how efficiently you produce energy, how quickly you recover and how resilient your immune system is.

Athletes don't have a different microbiome by accident. Their gut is tuned for performance. One of the most striking discoveries of recent years concerns Veillonella atypica: researchers analysed daily stool samples from Boston Marathon runners and found a significant rise in this bacterium after the race.

The mechanism is neat. Veillonella converts the lactate produced during exercise into propionate, a short-chain fatty acid that serves as an alternative energy source. Mice given Veillonella ran 13% longer on the treadmill.

Veillonella is only part of the picture, though. A 2025 systematic review of 19 studies identified sport-specific patterns in how the microbiome changes.

The link between gut bacteria and athletic performance is short-chain fatty acids (SCFAs): acetate, propionate and butyrate. Gut bacteria produce them when they ferment fibre, and they act on your metabolism at several levels:

• Acetate improves mitochondrial function and glucose metabolism in skeletal muscle
• Butyrate suppresses inflammation, strengthens the gut barrier and promotes the expansion of regulatory T cells, which matters for recovery
• Propionate serves as an alternative energy source and supports metabolic regulation

A study on dietary periodisation in highly trained athletes found that a high-carbohydrate diet improved time-trial performance by 6.5%. This correlated with a stable, healthy gut flora.

The microbiome's role in post-workout recovery is increasingly seen as relevant to performance. A study of rugby players found that athletes with higher microbial diversity had lower levels of systemic inflammation.

The anti-inflammatory functions of the microbiota help reduce DOMS (delayed-onset muscle soreness) and speed up recovery. In studies, probiotic strains such as L. plantarum PL-02 lowered creatine kinase and blood ammonia levels after exercise. Both are markers of muscle damage.

One finding stands out: a study of 543 athletes from different sports showed that each type of sport forms distinct microbial subgroups. Your gut literally adapts to your sport.

If you've had it, you won't forget it: cramps, nausea, an urgent need for a toilet in the middle of a race. Runner's gut, medically known as exercise-induced gastrointestinal syndrome (EIGS), affects 27% of marathon runners during the race and up to 96% of ultramarathon runners.

Several factors work together:

Here is the paradox. Acute exercise damages the gut barrier, yet regular training strengthens it in the long run. Trained cyclists have endotoxin levels at rest three times lower than non-athletes. The reasons: a better microbiota composition, more butyrate production and the induction of heat shock proteins.

Probiotics are a billion-euro market. But which strains actually have evidence behind them for athletes? A 2026 Bayesian meta-analysis gives the clearest answer so far: probiotic supplementation is linked to a moderate but practically meaningful improvement in athletic performance.

The strongest single-strain effect came from L. plantarum, with a standardised mean difference of 0.82. Multi-strain probiotics showed an effect of 0.45. Effective doses range from 10⁹ to 10¹¹ CFU per day.

Keep in mind that probiotic effects are strain- and dose-dependent. A generic "probiotic" from the supermarket won't improve your performance. The specific strains are what count.

The best investment in your microbiome is your plate, not an expensive supplement. The Mediterranean diet is considered the gold standard: plenty of plant foods, olive oil and polyphenols. It promotes the growth of Bifidobacterium, Faecalibacterium prausnitzii and Roseburia, exactly the bacteria that produce SCFAs and curb inflammation.

A randomised controlled trial with professional female footballers is particularly interesting. 200 ml of kefir a day for 28 days significantly increased microbial diversity, and VO₂max correlated with the abundance of SCFA-producing bacteria.

Your gut talks to your brain all the time, via the gut-brain axis. Gut bacteria produce neurotransmitters such as serotonin (around 95% of peripheral production), GABA and sleep-related metabolites.

For athletes, that has concrete effects:

• Sleep quality: a 2025 proof-of-concept study with elite athletes found that a multi-strain Lactobacillus consortium improved sleep quality and recovery, and improved the free testosterone/cortisol ratio
• Stress resilience: dysbiosis can overactivate the HPA axis and raise cortisol. Probiotics can dampen this overreaction
• Cognitive function: the gut-brain axis also affects focus and decision-making, which matters in long races

Sleep, stress and gut health are directly connected. Improve one and you benefit in all three.