Dietary intake and gastrointestinal integrity in runners undertaking high intensity exercise in the heat

Gastrointestinal disturbances are one of the most common issues for endurance athletes during training and competition in the heat. The relationship of typical dietary intake or nutritional interventions and perturbations in or maintenance of gut integrity is unclear. Twelve well-trained male endurance athletes (VO2max: 61.4  7.0 ml.kg.min-1) completed two trials in randomized order in 35C (Heat) and 21C (Thermoneutral) conditions, and kept a detailed nutritional diary for 8 consecutive days in between the two trials. The treadmill running trials consisted of 15 min at 60% VO2max, 15 min at 75% VO2max followed by 8 x 1 min high-intensity efforts. Venous blood samples were taken at baseline, at the end of each of the 3 exercise stages, and 1 h post exercise to measure gut integrity and permeability biomarker concentration for intestinal fatty acid binding protein (i-FABP), lipopolysaccharide (LPS), and lipopolysaccharide binding protein (LBP). The runners self-reported gut symptoms 1 h post- and 3 days post- exercise. The Heat condition induced large (45 to 370%) increases in i-FABP, LBP and LPS concentrations compared with baseline but induced mild gastrointestinal symptoms. Carbohydrate and polyunsaturated fat intake 24 h pre-exercise were associated with less LPS translocation. Protein, carbohydrate, total fat and polyunsaturated fat intake (8-day) were positively associated with the % increase of i-FABP in both conditions (0.62-0.93, -0.02 to 0.98; range of correlations, 95% CI). Typical nutrition intake partly explained increases in biomarkers and attenuation of symptoms induced by moderate and high intensity exercise under both heat and thermoneutral conditions.