title: Ingestion of a high-glycemic index meal increases muscle glycogen storage at rest but augments its utilization during subsequent exercise.
abstract: The aim of this study was to compare the effect of preexercise breakfast containing high- and low-glycemic index (GI) carbohydrate (CHO) (2.5g CHO/kg body mass) on muscle glycogen metabolism. On two occasions, 14 days apart, seven trained men ran at 71% maximal oxygen uptake for 30 min on a treadmill. Three hours before exercise, in a randomized order, subjects consumed either isoenergetic high- (HGI) or low-GI (LGI) CHO breakfasts that provided (per 70 kg body mass) 3.43 MJ energy, 175 g CHO, 21 g protein, and 4 g fat. The incremental areas under the 3-h plasma glucose and serum insulin response curves after the HGI meal were 3.9- (P < 0.05) and 1.4-fold greater (P < 0.001), respectively, than those after the LGI meal. During the 3-h postprandial period, muscle glycogen concentration increased by 15% (P < 0.05) after the HGI meal but remained unchanged after the LGI meal. Muscle glycogen utilization during exercise was greater in the HGI (129.1 +/- 16.1 mmol/kg dry mass) compared with the LGI (87.9 +/- 15.1 mmol/kg dry mass; P < 0.01) trial. Although the LGI meal contributed less CHO to muscle glycogen synthesis in the 3-h postprandial period compared with the HGI meal, a sparing of muscle glycogen utilization during subsequent exercise was observed in the LGI trial, most likely as a result of better maintained fat oxidation.
authors.affiliation: School of Sport and Exercise Sciences, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK.
authors.forename: Shiou-Liang
authors.initials: SL
authors.lastname: Wee
authors.forename: Clyde
authors.initials: C
authors.lastname: Williams
authors.forename: Kostas
authors.initials: K
authors.lastname: Tsintzas
authors.forename: Leslie
authors.initials: L
authors.lastname: Boobis
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D004040:Dietary Carbohydrates / Q000378:metabolism*; D005080:Exercise Test; D038321:Glycemic Index / Q000502:physiology*; D006003:Glycogen / Q000378:metabolism*; D006801:Humans; D008297:Male; D008657:Metabolic Clearance Rate; D018482:Muscle, Skeletal / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D019518:Postprandial Period / Q000502:physiology*; D012146:Rest / Q000502:physiology*
chemical_list: D004040:Dietary Carbohydrates; D006003:Glycogen