Carbohydrate intake during prolonged cycling minimizes effect of glycemic index of preexercise meal

We studied the effects of the glycemicindex (GI) of preexercise meals on metabolism and performance whencarbohydrate (CHO) was ingested throughout exercise. Six well-trainedcyclists performed three counterbalanced trials of 2-h cycling at~70% of maximal oxygen uptake, followed by a performance ride of 300 kJ. Meals consumed 2 h before exercise consisted of 2 g CHO/kg bodymass of either high-GI potato (HGI trial) or low-GI pasta (LGI trial), or of a low-energy jelly (Con trial). Immediately before and throughout exercise, subjects ingested a 10 g/100 mlU-¹⁴C]glucosesolution for a total of 24 ml/kg body mass. Despite differences inpreexercise glucose, insulin, and free fatty acids concentrations amongtrials, both total CHO oxidation for HGI, LGI, and Con trials,respectively, during steady-state exercise 403 ± 16, 376 ± 29, and 373 ± 24 (SE) g/2 h] andoxidation of the ingested CHO (65 ± 6, 57 ± 6, and 63 ± 5 g/2 h) were similar. There was no difference in time tocomplete the subsequent performance ride (946 ± 23, 954 ± 35, and 970 ± 26 s for HGI, LGI, and Con trials, respectively). WhenCHO is ingested during exercise in amounts presently recommended bysports nutrition guidelines, preexercise CHO intake has little effecton metabolism or on subsequent performance during prolonged cycling(~2.5 h).