Increased exogenous but unaltered endogenous carbohydrate oxidation with combined fructose-maltodextrin ingested at 120 g h(−1) versus 90 g h(−1) at different ratios

PURPOSE: This study aimed to investigate whether carbohydrate ingestion during 3 h long endurance exercise in highly trained cyclists at a rate of 120 g h(−1) in 0.8:1 ratio between fructose and glucose-based carbohydrates would result in higher exogenous and lower endogenous carbohydrate oxidation rates as compared to ingestion of 90 g h(−1) in 1:2 ratio, which is the currently recommended approach for exercise of this duration. METHODS: Eleven male participants (V̇O(2peak) 62.6 ± 7 mL kg(−1) min(−1), gas exchange threshold (GET) 270 ± 17 W and Respiratory compensation point 328 ± 32 W) completed the study involving 4 experimental visits consisting of 3 h cycling commencing after an overnight fast at an intensity equivalent to 95% GET. During the trials they received carbohydrates at an average rate of 120 or 90 g h(−1) in 0.8:1 or 1:2 fructose-maltodextrin ratio, respectively. Carbohydrates were naturally high or low in (13)C stable isotopes enabling subsequent calculations of exogenous and endogenous carbohydrate oxidation rates. RESULTS: Exogenous carbohydrate oxidation rates were higher in the 120 g h(−1) condition (120–180 min: 1.51 ± 0.22 g min(−1)) as compared to the 90 g h(−1) condition (1.29 ± 0.16 g min(−1); p = 0.026). Endogenous carbohydrate oxidation rates did not differ between conditions (2.15 ± 0.30 and 2.20 ± 0.33 g min(−1) for 120 and 90 g h(−1) conditions, respectively; p = 0.786). CONCLUSIONS: The results suggest that carbohydrate ingestion at 120 g h(−1) in 0.8:1 fructose-maltodextrin ratio as compared with 90 g h(−1) in 1:2 ratio offers higher exogenous carbohydrate oxidation rates but no additional sparing of endogenous carbohydrates. Further studies should investigate potential performance effects of such carbohydrate ingestion strategies.