Purpose: To determine whether combined ingestion of maltodextrin and fructose during 150 min of cycling exercise would lead to exogenous carbohydrate oxidation rates higher than 1.1 g·min−1.
Methods: Eight trained cyclists (V̇O2max: 64.1 ± 3.1 mL·kg·min−1) performed three exercise trials in a random order. Each trial consisted of 150 min cycling at 55% maximum power output (64.2 ± 3.5% V̇O2max) while subjects received a solution providing either 1.8 g·min−1 of maltodextrin (MD), 1.2 g·min−1 of maltodextrin + 0.6 g·min−1 of fructose (MD+F), or plain water. To quantify exogenous carbohydrate oxidation, corn-derived MD and F were used, which have a high natural abundance of 13C.
Results: Peak exogenous carbohydrate oxidation (last 30 min of exercise) rates were ∼40% higher with combined MD+F ingestion compared with MD only ingestion (1.50 ± 0.07 and 1.06 ± 0.08 g·min−1, respectively, P < 0.05). Furthermore, the average exogenous carbohydrate oxidation rate during the last 90 min of exercise was higher with combined MD+F ingestion compared with MD alone (1.38 ± 0.06 and 0.96 ± 0.07 g·min−1, respectively, P < 0.05).
Conclusions: The present study demonstrates that with ingestion of large amounts of maltodextrin and fructose during cycling exercise, exogenous carbohydrate oxidation can reach peak values of ∼1.5 g·min−1, and this is markedly higher than oxidation rates from ingesting maltodextrin alone.