Should Athletes Take Probiotics?
Some specific strains can calm gut symptoms and take the edge off colds during heavy training blocks, but no probiotic has been shown to directly boost speed, strength, or endurance performance.
Endurance training beats up the gut. Long runs and rides divert blood away from the intestines and raise gut permeability, and somewhere between 30 and 50 percent of endurance athletes deal with GI symptoms like cramping, bloating, or urgent bathroom stops during training and races. Since gut bacteria also talk to the immune system, the pitch for probiotics is straightforward: settle the gut, and symptoms, sickness, and maybe even performance should follow.
The catch is that probiotics isn’t a single product, it’s a category covering thousands of different strains, and the effects are strain- and dose-specific. A trial testing Lactobacillus plantarum 299v tells you close to nothing about how a random drugstore multi-strain blend performs, and reviews that pool dissimilar products together get exactly what you’d expect: noisy, inconsistent results. The 2019 International Society of Sports Nutrition position stand makes this the headline caveat of the entire field.
Where it holds up
The best-supported use case matches the mechanism: gut symptoms in endurance athletes. A 2022 systematic review of controlled trials found slight but real reductions in GI symptom counts and severity during training blocks with certain strains, though benefits mostly faded during actual races. On the immune side, a meta-analysis of 14 trials found probiotics lowered total respiratory-symptom severity scores and inflammatory markers like IL-6, with the clearest benefit in athletes under heavy training loads — though it found no reduction in how many colds athletes caught or how long each one lasted.
Where it’s thin
Direct performance enhancement doesn’t hold up: most controlled trials find no effect on strength, endurance, or race times, and reviewers can’t yet name a formulation that reliably works. Nutrient absorption is similarly unproven — a well-designed trial pairing L. plantarum 299v with iron showed a favorable trend in iron status for deficient female athletes, but it missed statistical significance.
If you’re prone to gut trouble in heavy training blocks or seem to catch every cold going around, a specific, studied strain taken consistently for a month or more is a reasonable, low-risk experiment. Just pick it based on the research, not the label.