Dose-response effects of ingested carbohydrate on exercise metabolism in women

• Published in: Medicine and science in sports and exercise Vol. 39; no. 1; pp. 131 - 138
• Main Authors: WALLIS, Gareth A, YEO, Sophie E, BLANNIN, Andrew K, JEUKENDRUP, Asker E
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD Lippincott Williams & Wilkins 2007
• Subjects: Adult; Biological and medical sciences; Exercise Test; Female; Fundamental and applied biological sciences. Psychology; Glucose - administration & dosage; Humans; Metabolism - physiology; Physical Endurance - physiology; Space life sciences; United Kingdom; Vertebrates: body movement. Posture. Locomotion. Flight. Swimming. Physical exercise. Rest. Sports; Physical exercise; Human; GLUCOSE INGESTION; Glucose; STABLE ISOTOPES; Metabolism; Ingestion; Sport; SUBSTRATE OXIDATION; ENDURANCE EXERCISE; Female; Endurance; Carbohydrate; Oxidation; Isotopes
• ISSN: 0195-9131; 1530-0315
• DOI: 10.1249/01.mss.0000241645.28467.d3

The effect of different quantities of carbohydrate (CHO) intake on CHO metabolism during prolonged exercise was examined in endurance-trained females.
On four occasions, eight females performed 2 h of cycling at approximately 60% .VO2max with ingestion of beverages containing low (LOW, 0.5 g.min(-1)), moderate (MOD, 1.0 g.min(-1)), or high (HIGH, 1.5 g.min(-1)) amounts of CHO, or water only (WAT). Test solutions contained trace amounts of [U-13C] glucose. Indirect calorimetry combined with measurement of expired 13CO2 and plasma 13C enrichment enabled calculation of exogenous CHO, liver-derived glucose, and muscle glycogen oxidation during the last 30 min of exercise.
The highest rates of exogenous CHO oxidation were observed in MOD, with no further increases in HIGH (peak rates of 0.33 +/- 0.02, 0.50 +/- 0.03, and 0.48 +/- 0.05 g.min(-1) for LOW, MOD, and HIGH, respectively; P < 0.05 for LOW vs MOD and HIGH). Endogenous CHO oxidation was lowest in MOD (0.99 +/- 0.06, 0.82 +/- 0.08, 0.70 +/- 0.07, and 0.89 +/- 0.09 g.min(-1); P < 0.05 for MOD vs all other trials). Compared with WAT, CHO ingestion reduced liver glucose oxidation during exercise by approximately 30% (P < 0.05 for WAT vs all CHO). Differential rates of muscle glycogen oxidation were observed with different CHO doses (0.57 +/- 0.07, 0.53 +/- 0.08, 0.41 +/- 0.07, and 0.60 +/- 0.09 g.min(-1) for WAT, LOW, MOD, and HIGH respectively; P < 0.05 for MOD vs HIGH).
In endurance-trained women, the highest rates of exogenous CHO oxidation and greatest endogenous CHO sparing was observed when CHO was ingested at moderate rates (1.0 g.min(-1), 60 g.h(-1)) during exercise.