EFFECT OF CARBOHYDRATE INGESTION ON GLUCOSE KINETICS DURING EXERCISE

Six well-trained men (peak pulmonary oxygen uptake = 5.03 +/- 0.11 1/m in) were studied during 2 h of exercise at 69 +/- 1% peak pulmonary ox ygen uptake to examine the effect of carbohydrate (CHO) ingestion on g lucose kinetics. Subjects ingested 250 ml of either a 10% glucose solu tion containing 6-[H-3]glucose (CHO) or a sweet placebo every 15 min d uring exercise. Glucose kinetics were assessed by 6,6-[H-2]glucose inf usion corrected for gut-derived glucose in CHO. Plasma glucose was hig her (P < 0.05) in CHO from 20 min. Total glucose appearance was higher in CHO due to glucose delivery from the gut (68 +/- 7 g), since hepat ic glucose production was reduced by 51% (29 +/- 5 vs. 59 +/- 5 g). Gl ucose uptake was higher in CHO (96 +/- 7 vs. 60 +/- 6 g) with the inge sted glucose supplying 67 +/- 4 g and, with the assumption that it was fully oxidized, accounted for 14 +/- 1% of total energy expenditure. In conclusion, CHO ingestion during prolonged exercise results in supp ression of hepatic glucose production and increased glucose uptake. Th ese effects appear to be mediated mainly by increased plasma glucose a nd insulin levels.