The effect of glycemic index on plasma glucose and lactate levels during incremental exercise

Consumption of low glycemic index (GI) foods before submaximal endurance ex ercise may be beneficial to performance. To test whether this may also be t rue for high intensity exercise, 10 trained cyclists began an incremental e xercise test to exhaustion 65 min after consuming equal carbohydrate portio ns of glucose (HGI), pasta (LGI), and a noncarbohydrate control (PL). Time to fatigue: did not differ significantly (p = 0.05) between treatments. Pla sma glucose concentration was significantly lower after LGI vs. HGI from 15 to 45 min of rest postprandial. During exercise, plasma glucose concentrat ion was significantly lower after HGI vs. LGI from 200 W until exhaustion. Plasma lactate concentration following HGI was significantly higher than PL from 30 min of rest postprandial through to the end of the 200-W workload. Plasma lactate concentration following LGI was significantly lower than af ter HGI from 45 min of rest postprandial through to the end of the 100-W wo rkload. At higher exercise intensities, there was no significant difference in plasma lactate levels between treatments. These findings suggest that a high GI carbohydrate meal (1 g/kg body wt) 65 min prior to exercise decrea ses plasma glucose and increases plasma lactate levels compared to a low GI meal, but not enough to be detrimental to incremental exercise performance .