Duathlon performance unaltered by short-term changes in dietary fat and carbohydrates.

PURPOSE: This study investigated the effects of short-term dietary changes on metabolism and duathlon performance. METHODS: Eleven men underwent a high-fat (HF; >65% fat from energy) or a high-carbohydrate (CHO; HC) diet (>60% CHO from energy). Energy intake was individualized, and commercially available foods were prepared and packaged for each participant 48 hr before they completed a laboratory-based duathlon (5-km run, 30 km cycling, and 10-km run). Blood samples were obtained before, immediately after, and 1 and 2 hr after the duathlon for determination of glucose, insulin, and glucagon. Oxygen consumption, ratings of perceived exertion (RPE), and respiratory-exchange ratio were assessed, and fat and CHO oxidation were estimated before, during, and after the duathlon. RESULTS: Dietary records indicated a significant difference in fat content ingested before the duathlons (p < .05). Time to complete the duathlon did not differ between the HC- and the HF-diet trials. CHO-oxidation rate was higher during the HC-diet trial than during the HF-diet trial (p = .006). Fat-oxidation rates were higher in the HF-diet trial than in the HC-diet trial (p = .001). No differences in RPE were found between dietary trials. Blood glucose concentration was higher immediately after the duathlon in the HC-diet trial than in the HF-diet trial and remained higher 1 and 2 hr after the duathlon (p < .05). CONCLUSION: Duathlon performance was not altered by short-term changes in dietary fat or CHO composition despite higher blood glucose concentrations under the HC condition.

Initial metabolic state and exercise-induced endotoxaemia are unrelated to gastrointestinal symptoms during exercise.

The aim of the study was to investigate the association between the initial metabolic state and exercise-induced endotoxaemia on the appearance of gastrointestinal symptoms (GIS) during exercise. Eleven males (36.6 ± 4.9 yrs, 1.7 ± 0.1 m, 74.5 ± 7.7 kg, DEXA body fat % 17.2 ± 6.6, VO2max 57.4 ± 7.4 ml·kg(-1)·min(-1)) underwent two isoenergetic diets designed to change their initial metabolic status by either depleting or maintaining their hepatic and muscular glycogen content. These diets and accompanying exercise sessions were performed by each participant in the days before completing a laboratory-based duathlon (5-km run, 30-km cycling, 10-km run). Blood samples were obtained before, immediately and 1- and 2-h following the duathlon for determination of insulin (IN), glucagon (GL), endotoxin, aspartic aminotransferase (AST), and alanine aminotransferase (ALT) markers. GIS were assessed by survey before and after exercise. Diet content produced a different energy status as determined by macronutrient content and the IN/GL ratio (p < 0.05), and mild exercise-induced endotoxaemia was observed in both experimental duathlons. Regardless of the diet, the AST/ALT ratio following exercise and in the recovery phase indicated hepatocyte and liver parenchyma structural damage. In spite of GIS, no significant correlations between endotoxin levels and GIS were found. In conclusion, increased markers of endotoxaemia observed with the high-intensity exercise were unrelated to hepatic function and/or GIS before and after exercise. Key pointsGastrointestinal symptoms before, during, and after a competition are reported by approximately 20%-50% of the athletes participating in endurance events such as marathon, cycling and triathlon.Energy status, exercise-induced endotoxaemia and liver structural damage might be related to gastrointestinal symptoms.In this study, gastrointestinal symptoms observed before and after endurance exercise were unrelated to endotoxin levels or hepatic structural damage.