Prebiotic Bimuno ^® GOS reduces illness symptoms and supports gut barrier function and immunity after intermittent exercise in the heat

Exercise in hot climates increases the risk of gastrointestinal (GI) disruption and respiratory illness. We investigated the effects of a 42 day prebiotic intervention on markers of intestinal epithelial injury, GI discomfort and immunity following football specific exercise in the heat and daily upper respiratory illness. Twenty-six team-sport male athletes were randomized to receive 3.65 (2.75 active galactooligosaccharide) gday^-1 of either Bimuno galactooligosaccharide (Bimuno^® GOS; n = 13) or a maltodextrin placebo (Placebo; n = 13) for 42 days in a double-blind parallel group design. At days 0 and 42 of each intervention, participants completed the football specific intermittent treadmill protocol in 33°C and 50% relative humidity. Blood, saliva and GI symptoms were collected at days 0 and 42 for the assessment of plasma intestinal fatty acid binding protein, lipopolysaccharide binding protein, salivary immunoglobulin A (sIgA) and GI discomfort. Participants also completed questionnaires for self-reported upper respiratory and gastrointestinal symptoms (daily and weekly, respectively), over the 42 days. At day 42, there was a reduction in pre-full-time change in plasma intestinal fatty acid binding protein and severity of GI discomfort in the Bimuno^® GOS group compared with Placebo, but no change in lipopolysaccharide binding protein. The day 0-42 change in sIgA secretion rate after the football specific intermittent treadmill protocol was higher in the Bimuno^® GOS than the Placebo group, and during the 42 days there was a reduction in upper respiratory symptom duration and severity in the Bimuno^® GOS group compared with Placebo. In team-sport athletes, 42 days of supplementation with prebiotic Bimuno^® GOS can alleviate GI disruption and better maintain sIgA secretion rate in response to football specific activity in the heat, whilst also reducing the duration and severity of upper respiratory symptoms.