Oxidation of combined ingestion of maltodextrins and fructose during exercise

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 (VO2max: 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% VO2max) 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 C-13. Results: Peak exogenous carbohydrate oxidation (last 30 min of exercise) rates were similar to40% 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 similar to1.5 g(.)min(-1), and this is markedly higher than oxidation rates from ingesting maltodextrin alone.