Influence of diet on leg uptake of glucose during heavy exercise

Four young men each performed three treadmill walks to exhaustion at 70% of their respective O2 uptake maxima. Each walk followed 3 days consumption of either a normal mixed (M), high fat and protein (F-P), or high carbohydrate (CHO) diet. The fractional use of carbohydrates for energy during the initial 1/2-hr of work was significantly reduced following the F-P diet as compared with the M or CHO diets (P less than 0.005), averaging 38.2% (F-P), 69.9% (M), and 71.9 (CHO). Carbohydrates energy production was negatively correlated with blood levels of both free fatty acids ( r = -0.62, P less than 0.05) and beta-OH-butyrate (r = - 0.79, P less than 0.005). Work time to exhaustion was closely correlated with the fractional usage of carbohydrates for energy (r = 0.86, P less than 0.001). The femoral arteriovenous blood glucose difference was directly related to the pre-work dietary carbohydrate fraction, with the 30-min work means 0.25 mM (F-P), 0.34 mM (M), and 0.52 mM (CHO). Estimation of leg arteriovenous O2 difference indicated that leg uptake of blood-borne glucose provided approximately 23 +/- 10% (F-P), 30 +/- 8% (M), and 46 +/- 13% (CHO) of the legs' aerobic substrate during the first 30 min of work. These results provide further evidence for the shift from noncarbohydrate to carbohydrate energy sources during exercise as the carbohydrate fraction of the diet is elevated.