Optimal immune function is emerging as a key contributor to sporting performance (Berg et al. Exerc Immunol Rev,1999, 5, 78-95). There is increasing scientific interest in the prevention and management of gastrointestinal (GI) illness in athletes travelling to countries with varied diet and sanitation conditions. This study aims to examine the effectiveness of probiotic supplementation in altering gut flora and preventing travelers` diarrhea (TD) in elite athletes traveling to a highrisk country. Eight athletes were supplemented for 8 weeks with Lactobacillus acidophilus, Bifidobacteria lactis, and Lactobacillus rhamnosus (1/day). Stool samples were taken at baseline, directly before traveling (~2 weeks later), and at return. Fluorescent in situ hybridization was used to assess bacterial concentrations of total eubacteria, bifidobacteria, and bacteroides (log10 bacteria/g fresh feces), and gas chromatography to assess short-chain fatty acid (SCFA) concentrations (mmol/g fresh feces), of three fecal samples taken at baseline, precompetition, and postcompetition. Participants used a daily log to record symptoms of TD, classified using the World Health Organization (WHO) definition of =3 loose or watery stools in a 24-hr period (Allen et al., Cochrane Review, 2009, 1, 1-72). There were no statistical changes to total eubacteria, bifidobacteria, bacteroides, or SCFA concentrations, but there was a trend towards an increase for all bacterial groups from baseline to precompetition. Statistically significant relationships (p = .05) were also detected between average bifidobacteria and n-valeric concentration (r = .520) and average bacteroide and n-butyrate concentration (r = -.557). Fifty percent of athletes reported TD symptoms. Probiotic supplementation led to small modulations in athlete gut flora that may be clinically relevant to health and indirectly to performance. Supplementation was unable to prevent episodes of TD in 50% of athletes.
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