Probiotics & Gut Microbiota: Evidence for Athletes

Why this review matters

Marttinen and colleagues (Nutrients, 2020) synthesised the clinical evidence connecting gut microbiota composition, probiotic supplementation and physical performance in athletes and physically active populations. Beyond cataloguing studies, they unpack the mechanisms — SCFA production, barrier integrity, immune modulation — through which microbes shape what an athlete can do on the field.

The athlete microbiome looks different

Across cross-sectional studies, athletes and physically active subjects show greater faecal microbial diversity and higher abundance of health-associated genera such as Akkermansia, Veillonella and Prevotella than sedentary controls. Functional pathways linked to amino acid and carbohydrate metabolism are upregulated — useful machinery for athletes who need fast fuel turnover during and after sessions.

SCFAs: the metabolic bridge

Gut bacteria ferment non-digestible carbohydrates into short-chain fatty acids — primarily acetate, propionate and butyrate. Butyrate fuels colonic epithelial cells and reinforces the gut barrier; acetate reaches muscle tissue and can cross the blood-brain barrier; propionate serves as a substrate for hepatic gluconeogenesis. Regular training raises faecal SCFA content, and preclinical work identifies SCFAs as direct modulators of physical performance.

The gut–muscle axis runs both ways

One of the review's clearest points: the relationship is bidirectional. Lactate produced by skeletal muscle during anaerobic work crosses into the colonic lumen, where lactate-utilising species ferment it back into propionate that benefits the host. The athlete feeds the bacteria; the bacteria feed the athlete.

Where probiotics fit in

Probiotics are live microorganisms that — at adequate doses — confer a health benefit. In athletes, the documented benefits cluster around:

• Immunity: reduced incidence and duration of upper respiratory tract infections during heavy training blocks.
• GI tolerance: fewer exercise-induced GI symptoms (cramps, urgency, diarrhoea) that derail endurance sessions and competition days.
• Barrier and inflammation: improved gut barrier integrity and reduced systemic inflammatory load after strenuous bouts.
• Recovery and availability: indirectly more healthy training days — itself a performance lever over a season.

Effects are strain-specific

The International Society of Sports Nutrition's position stand — echoed by the review — is unambiguous: probiotic effects in athletes are strain-specific, not species-level and definitely not generic. A Lactobacillus rhamnosus strain that improves immunity in runners cannot be assumed equivalent to a different L. rhamnosus strain on the shelf. Strain identity, dose and timing matter.

What's still missing

High-quality, adequately powered RCTs in elite athletes remain rare. Most existing trials are short, small, and use mixed analytical methods — limitations the authors flag explicitly. The roadmap: longer interventions, species- and strain-resolved sequencing, and clearer mechanistic readouts connecting microbiome shifts to performance metrics rather than surrogate markers alone.

Practical translation

For performance teams the message is pragmatic. Profile the athlete's microbiome at species level. Use targeted probiotic strains where strain-specific evidence exists. Pair supplementation with fibre-rich, periodised nutrition so the resident community has the substrates it needs. And measure — not just symptoms, but the microbiome itself, repeatedly, across the season. For the broader picture of how exercise and microbes co-evolve, read our summary of the 2022 Sports Medicine review on the athlete gut microbiome.

Reference: Marttinen M, Ala-Jaakkola R, Laitila A, Lehtinen MJ. Gut Microbiota, Probiotics and Physical Performance in Athletes and Physically Active Individuals. Nutrients. 2020;12(10):2936. doi.org/10.3390/nu12102936