Moncanda-Jimenez, J., Plaisance, E. P., Mestek, M. L., Ratcliff, L., Araya-Ramirez, F., Taylor, J. K., Grandjean, P. W., & Aragon Vargas, L. F. (20008). Short-term changes in dietary nutrient composition fail to modify duathlon performance. ACSM 55th Annual Meeting Indianapolis. Presentation number 852.

This study investigated the effect of short-term changes in dietary nutrient composition on metabolism and duathlon performance. Males (N = 11) underwent two individual isoenergetic diets designed to either deplete (carbohydrates 21.3%, fat 67.6%, protein 11.4%) or maintain (carbohydrates 63.5%, fat 25.4%, protein 11.2%) their hepatic and muscular glycogen content. The diets and exercise sessions were followed two-days before completing a laboratory-based duathlon (5-km run, 30-km cycling, 10-km run). Blood samples were obtained before, immediately after and one and two hours following the duathlon to measure glucose. VO2, carbohydrate and fat oxidation rates, and ratings of perceived exertion were measured before and during the duathlons.

Dietary records indicated a significant difference in carbohydrate and fat content ingested before the duathlons. Time to complete the duathlon did not differ between the high and the low carbohydrate diet trials. Carbohydrate oxidation rate was higher during the high-carbohydrate diet trial than during the low-carbohydrate diet trial. Fat oxidation rates were higher in the low-carbohydrate diet trial compared to the high-carbohydrate diet trial. Regardless of the dietary trial, Ss performed the duathlon at approximately 70% of their individual VO2max. No differences in ratings of perceived exertion were found between dietary trials. Blood glucose concentration was higher immediately following the duathlon in the high-carbohydrate diet trial, than in the low-carbohydrate diet trial, and remained higher for more than two hours following the duathlon.

Implication. Duathlon performance was not altered by changes in dietary carbohydrate or fat composition despite higher blood glucose concentrations under the high-carbohydrate diet.

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