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

We studied the effects of the glycemic index (GI) of preexercise meals on m etabolism and performance when carbohydrate (CHO) was ingested throughout e xercise. Six well-trained cyclists performed three counterbalanced trials o f 2-h cycling at similar to 70% of maximal oxygen uptake, followed by a per formance ride of 300 kJ. Meals consumed 2 h before exercise consisted of 2 g CHO/kg body mass of either high-GI potato (HGI trial) or low-GI pasta (LG I trial), or of a low-energy jelly (Con trial). Immediately before and thro ughout exercise, subjects ingested a 10 g/100 mi [U-C-14]glucose solution f or a total of 24 ml/kg body mass. Despite differences in preexercise glucos e, insulin, and free fatty acids concentrations among trials, both total CH O oxidation for HGI, LGI, and Con trials, respectively, during steady-state exercise [403 +/- 16, 376 +/- 29, and 373 +/- 24 (SE) g/2 h] and oxidation of the ingested CHO (65 +/- 6, 57 +/- 6, and 63 +/- 5 g/2 h) were similar. There was no difference in time to complete the subsequent performance rid e (946 +/- 23, 954 +/- 35, and 970 +/- 26 s for HGI, LGI, and Con trials, r espectively). When CHO is ingested during exercise in amounts presently rec ommended by sports nutrition guidelines, preexercise CHO intake has little effect on metabolism or on subsequent performance during prolonged cycling( similar to 2.5 h).