The ingestion of protein with a maltodextrin and fructose beverage on substrate utilisation and exercise performance

The study investigated the ingestion of maltodextrin, fructose, and protein on exogenous carbohydrate oxidation (CHOEXO) and exercise performance. Seven trained cyclists and (or) triathletes (maximal oxygen consumption, 59.20 ± 9.00 mL · kg(-1) · min(-1)) performed 3 exercise trials that consisted of 150 min of cycling at 50% maximal power output (160 ± 11 W), followed by a 60-km time trial. One of 3 beverages were randomly assigned during each trial and consumed at 15-min intervals: (i) 0.84 g · min(-1) maltodextrin + 0.52 g · min(-1) fructose + 0.34 g · min(-1) protein (MD+F+P); (ii) 1.10 g · min(-1) maltodextrin + 0.60 g · min(-1) fructose (MD+F); or (iii) 1.70 g · min(-1) maltodextrin (MD). CHO(EXO) and fuel utilisation were assessed via measurement of expired air (13)C content and indirect calorimetry, respectively. Mean total CHO oxidation (CHOTOT) rates were 2.35 ± 0.18, 2.76 ± 0.08, and 2.61 ± 0.17 g · min(-1) with MD, MD+F, and MD+F+P, respectively, although not significantly different. Peak CHO(EXO) rates with MD+F were significantly greater by 41.4% (p = 0.001) and 45.4% (p = 0.0001) compared with MD+F+P and MD, respectively (1.57 ± 0.22 g · min(-1), 1.11 ± 0.08 g · min(-1), and 1.08 ± 0.11 g · min(-1), respectively). Performance times were 2.2% and 5.0% faster with MD+F compared with MD+F+P and MD, respectively; however, they were not statistically significant. Ingestion of an MD-fructose-protein commercial sports beverage significantly reduced peak and mean CHO(EXO) rates compared with MD+F, but did not significantly influence CHOTOT. The addition of protein to an MD+F beverage did not enhance performance times.