The study aimed to determine the effects of 24-h high (HFOD) and low (LFOD) fermentable oligo-, di-, monosaccharide, and polyol (FODMAP) diets before exertional heat stress on gastrointestinal integrity, function, and symptoms. Eighteen endurance runners consumed a HFOD and a LFOD (double-blind crossover design) before completing 2 h of running at 60% maximal oxygen uptake in 35 °C ambient temperature. Blood samples were collected before and after exercise to determine plasma cortisol and intestinal fatty acid binding protein (I-FABP) concentrations, and bacterial endotoxin and cytokine profiles. Breath hydrogen (H2) and gastrointestinal symptoms (GIS) were determined pre-exercise, every 15 min during, and in recovery. No differences were observed for plasma cortisol concentration between diets. Plasma I-FABP concentration was lower on HFOD compared with LFOD (p = 0.033). A trend for lower lipopolysaccharide binding protein (p = 0.088), but not plasma soluble CD14 (p = 0.478) and cytokine profile (p > 0.05), responses on HFOD was observed. A greater area under the curve breath H2 concentration (p = 0.031) was observed throughout HFOD (mean and 95% confidence interval: HFOD 2525 (1452–3597) ppm·4 h−1) compared with LFOD (1505 (1031–1978) ppm·4 h−1). HFOD resulted in greater severity of GIS compared with LFOD (pre-exercise, p = 0.017; during, p = 0.035; and total, p = 0.014). A 24-h HFOD before exertional heat stress ameliorates disturbances to epithelial integrity but exacerbates carbohydrate malabsorption and GIS severity in comparison with a LFOD. Novelty Twenty-four-hour high FODMAP diet ameliorated disturbances to gastrointestinal integrity. Twenty-four-hour high FODMAP diet results in greater carbohydrate malabsorption compared with low FODMAP diet. Incidence of GIS during exertional heat stress were pronounced on both low and high FODMAP diets, but greater GIS severity was observed with high FODMAP diet.
- Dietary intake
- Gastrointestinal symptoms