Effects of meals with a different glycemic index on respiratory and biochemical outcomes during endurance exercise

The purpose of this study was to compare the effects of a pre-exercise meal containing a different glycemic index on the endurance exercise performance and biochemical outcomes. Twelve healthy volunteers consumed a high glycemic index meal (74, HGI), a low glycemic index meal (32.8, LGI) (each meal provided 1 g carbohydrate/kg body weight), or water (as the control) 1 h before running at 65% VO ₂max to exhaustion. After ingesting the meal, blood samples of subjects were drawn from a vein at the baseline, at 15, 30, 45, and 60 min, and at exhaustion. The heart rate, rating perceived exercise (RPE), and respiratory metabolism exchange ratio (RER) were recorded during the exercise. As the data showed, RER values of the LGI and HGI groups were higher than the control before exercise (p <0.05). There were no significant differences among the three groups for heart rate, RPE, and time to exhaustion. Ingestion of the HGI and LGI meals resulted in hyperglycemia during the postprandial period compared to the control (p <0.05). The concentration of plasma free fatty acids (FFAs) in the HGI and LGI groups were significantly lower than in the control (p <0.05). The concentration of FFAs in the LGI group was significantly lower than that in the HGI group. In conclusion, this study demonstrated that an LGI meal might have a positive effect on aerobic endurance through contributing energy by providing carbohydrates as fuel. However, with an HGL meal, one might observe the phenomena of delayed production of factors which cause fatigue, and enhanced endurance exercise performance may be seen with ingestion of an LGI meal before exercise.