Gastrointestinal complaints are common among endurance athletes, especially runners and triathletes. Most of these problems are due to altered blood flow away from the gut to working muscles. Reduced intestinal blood flow as well as increased core temperature can damage the intestinal lining (mucosa), disrupting the tightly regulated intestinal barrier and lead to a systemic inflammatory response.

Also known as leaky gut, increased intestinal wall permeability causes what is known as endotoxemia, or self-poisoining, when the disease-causing and toxic contents of the small intestine are leaked into the bloodstream and surrounding tissues. This increases an athlete’s susceptibility to infectious and autoimmune diseases.(1,2)

Immediate symptoms of GI upset include nausea, stomach/intestinal cramps, vomiting and diarrhea. Repeated episodes of GI inflammation may lead to a number of other conditions most notably autoimmune dieases.(3)

Probiotics are live bacteria that have beneficial effects in our digestive tract and influence our overall health. It’s estimated the human GI tract contains roughly 100 trillion organisms (which is 10 times the amount of actual human cells in the entire body!)(4) Probiotics are easily obtained as nutritional supplements, however quality and potency can vary widely.
(Normally, we cultivate our own probiotics through a healthy diet containing soluble fiber, fermented and cultured foods.)

Because probiotics have been shown to be helpful in a number of other sport-related health conditions (such as number and severity of respiratory tract infections, inflammation, oxidation and general GI complaints), researchers are looking at how probiotic supplementation can prevent leaky gut and its consequences.

Several studies show that different strains of probiotics can improve intestinal lining function in athletes.(5) A small but interesting study looked at how probiotics would offset the effects of running performance in a heated environment.  This study was based on the idea that probiotics might prevent the negative effects of exercise-induced leaky gut while running in the heat. The researchers noted only slight improvements in the measurement of leaky gut-associated proteins and a slight reduction in GI symptoms. However, they also noted a significant improvement in run time to fatigue, meaning the runners were able to run at a given pace for longer than usual after taking the probiotics for a period of time (4 weeks). They weren’t sure exactly how this occurred, but it’s interesting regardless.

The take home message is that while there’s a lot of research to do on probiotics and their effects on our health, there’s good enough evidence to show that it’s probably important for endurance athletes to supplement with a probiotic to prevent leaky gut and its consequences. 

1. Lambert GP. Stress-induced gastrointestinal barrier dysfunction and its inflammatory effects. J Anim Sci. 2009;87(E.Suppl):E101–E108.

2. West NP, Pyne DB, Peake JM, Cripps AW. Probiotics, immunity and exercise: a review. Exerc Immunol Rev. 2009;15:107–126.

3. Fasano A. Leaky gut and autoimmune diseases. Clinic Rev Allerg Immunol. 2012;42:71–78.

4. Sears CL.  A dynamic partnership: celebrating our gut flora. Anaerobe. 2005 Oct;11(5):247-51.

5. Lamprecht M, Bogner S, Schippinger G, Steinbauer K, Fankhauser F, Hallstroem S, Schuetz B, Greilberger JF. Probiotic supplementation affects markers of intestinal barrier, oxidation, and inflammation in trained men; a randomized, double-blinded, placebo-controlled trial. J Int Soc Sports Nutr. 2012 Sep 20;9(1):45.