Gut health & sport: How your microbiome affects performance

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

Current multi-omics research (2024–2026) shows a bidirectional relationship between training and the microbiome: endurance training changes the microbial composition, while microbial metabolites, known as short-chain fatty acids (SCFAs), influence energy metabolism, immunity and recovery.

For athletes, this means your gut is not a passive digestive tube but an active training partner. It helps determine how efficiently you produce energy, how quickly you recover and how resilient your immune system is.

Athletes do not simply have a different microbiome by chance. Their gut is tuned for performance. One of the most groundbreaking discoveries of recent years concerns Veillonella atypica: researchers analysed daily stool samples from Boston Marathon runners and found a significant increase in this bacterium after the race.

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

But Veillonella is only part of the picture. A 2025 systematic review of 19 studies identified sport-specific patterns in microbiome modulation.

The link between gut bacteria and athletic performance is short-chain fatty acids (SCFAs): acetate, propionate and butyrate. They are produced when gut bacteria ferment fibre and influence your metabolism on 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 is important 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 microbiota.

The role of the microbiome in post-workout recovery is increasingly recognised as relevant to performance. A study involving rugby players found that athletes with greater microbial diversity had lower levels of systemic inflammation.

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

Interestingly, a study of 543 athletes from different sports found that the type of sport shapes distinct microbial subgroups. Your gut literally adapts to your sport.

If you have experienced it, you will not forget it: cramps, nausea, the 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 a race and up to 96% in ultramarathons.

It is caused by several factors working together:

Here is the paradox: while acute exercise damages the gut barrier, chronic training strengthens it over the long term. Trained cyclists show endotoxin levels at rest that are three times lower than those of non-athletes. The mechanisms include a better microbiota composition, increased butyrate production and heat-shock protein induction.

Probiotics are a billion-pound market, but which strains actually have evidence for athletes? A Bayesian meta-analysis from 2026 provides the clearest answer to date: probiotic supplementation is associated with a moderate but practically meaningful improvement in athletic performance.

The strongest single-strain effect was found for 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.

Importantly, probiotic effects are strain- and dose-dependent. A generic "probiotic" from the supermarket will not improve performance. The specific strains are what matter.

The best investment in your microbiome is not an expensive supplement, but what is on your plate. The Mediterranean diet is considered the gold standard: rich in plant-based foods, olive oil and polyphenols. It promotes the growth of Bifidobacterium, Faecalibacterium prausnitzii and Roseburia, the very bacteria that produce SCFAs and inhibit inflammation.

Particularly interesting: an RCT in professional female footballers showed that 200 mL of kefir daily for 28 days significantly increased microbial diversity, while VO₂max correlated with the abundance of SCFA-producing bacteria.

Your gut is constantly communicating with your brain via the gut-brain axis. Gut bacteria produce neurotransmitters such as serotonin (around 95% of peripheral production), GABA and sleep-related metabolites.

For athletes, this has tangible effects:

• Sleep quality: A 2025 proof-of-concept study involving elite athletes showed that a multi-strain Lactobacillus consortium improved sleep quality and training recovery, while optimising the free testosterone-to-cortisol ratio
• Stress resilience: Dysbiosis can hyperactivate the HPA axis and increase cortisol. Probiotics may dampen this excessive response
• Cognitive function: The gut-brain axis also affects focus and decision-making, which matters in long competitions

Sleep, stress and gut health are therefore directly linked. Improving one can benefit all three areas.