Abstract
PurposeTo examine the dose–response effects of acute glutamine supplementation on markers of gastrointestinal (GI) permeability, damage and, secondary, subjective symptoms of GI discomfort in response to running in the heat.MethodsTen recreationally active males completed a total of four exercise trials; a placebo trial and three glutamine trials at 0.25, 0.5 and 0.9 g kg−1 of fat-free mass (FFM) consumed 2 h before exercise. Each exercise trial consisted of a 60-min treadmill run at 70% of dot {V}{{text{O}}_{{text{2max}}}} in an environmental chamber set at 30 °C. GI permeability was measured using ratio of lactulose to rhamnose (L:R) in serum. Plasma glutamine and intestinal fatty acid binding protein (I-FABP) concentrations were determined pre and post exercise. Subjective GI symptoms were assessed 45 min and 24 h post-exercise.ResultsRelative to placebo, L:R was likely lower following 0.25 g kg−1 (mean difference: − 0.023; ± 0.021) and 0.5 g kg−1 (− 0.019; ± 0.019) and very likely following 0.9 g kg− 1 (− 0.034; ± 0.024). GI symptoms were typically low and there was no effect of supplementation.DiscussionAcute oral glutamine consumption attenuates GI permeability relative to placebo even at lower doses of 0.25 g kg−1, although larger doses may be more effective. It remains unclear if this will lead to reductions in GI symptoms. Athletes competing in the heat may, therefore, benefit from acute glutamine supplementation prior to exercise in order to maintain gastrointestinal integrity.
Highlights
Gastrointestinal (GI) discomfort is frequently reported by endurance athletes in long-distance events such as marathons and triathlons (Gil et al 1998)
Athletes competing in the heat may, benefit from acute glutamine supplementation prior to exercise in order to maintain gastrointestinal integrity
While it has been previously shown that a large, acute dose of glutamine (0.9 g kg−1 fat-free mass (FFM)) is able to attenuate exerciseinduced increases in intestinal permeability (Zuhl et al 2015), we report for the first time that lower doses
Summary
Gastrointestinal (GI) discomfort is frequently reported by endurance athletes in long-distance events such as marathons and triathlons (Gil et al 1998). Decreased splanchnic perfusion and increased small intestinal permeability, defined as the non-mediated diffusion of large normally restricted molecules from the intestinal lumen to the blood (Lambert 2009), have been postulated as key mechanisms (van Wijck et al 2012). Water and molecules through the paracellular pathway is regulated by the tight junctions of the epithelia (Gonzalez-Mariscal et al 2003), and consequent disruption of these tight junctions during exercise can lead to increased intestinal permeability allowing passage of both small and large molecules. Lipopolysaccharide (LPS) endotoxins are found in large quantities in the human gut (van Deventer et al 1988) and increased circulating LPS levels in athletes have been found to be associated with GI symptoms including nausea, vomiting and diarrhoea (Jeukendrup et al 2000). Recent investigations have examined the efficacy of nutritional strategies such as colostrum, probiotics and glutamine in an attempt to lessen such gastrointestinal disruption (Marchbank et al 2011; Shing et al 2014; Zuhl et al 2014b)
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