DA: Journal of American Physiological Society
Ingestion of a high-glycemic index meal increases muscle glycogen storage at rest but augments its utilization during subsequent exercise
Shiou-Liang Wee,1 Clyde Williams,1 Kostas Tsintzas,2 and Leslie Boobis3
1Sports and Exercise Nutrition Research Group, School of Sport and Exercise Sciences, Loughborough University, Loughborough; 2Centre for Integrated Systems Biology and Medicine, School of Biomedical Sciences, Nottingham University, Nottingham; and 3Sunderland Royal Hospital, Sunderland, United Kingdom
Submitted 8 November 2004 ; accepted in final form 12 April 2005
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.
In summary, our findings indicate that:
1) a HGI meal results in greater muscle glycogen storage than a LGI meal in overnight fasted subjects with normal glycogen concentration;
2) the relative shift in substrate metabolism during 30 min of exercise from CHO to fat after ingestion of a LGI compared with a HGI meal was accompanied by a reduction in the rate of muscle glycogen utilization and not blood glucose oxidation; and
3) compared with MG, concentrations of PG appear to be more sensitive to feeding and exercise when total glycogen is not supercompensated or depleted.
However, the greater fat oxidation and lower muscle glycogen utilization after the LGI meal may not always translate to a greater endurance capacity than after the HGI meal, as indicated by the inconsistency in the literature regarding the ergogenic effects of LGI or MGI meals over high GI meals. Further studies are required to investigate the relative roles of muscle and liver glycogen in energy metabolism and the onset of fatigue during exercise performed after ingestion of meals with different glycemic indexes.
FONTE: http://jap.physiology.org/content/99/2/707.full.pdf+html
in allegato c'è lo studio completo
Ingestion of a high-glycemic index meal increases muscle glycogen storage at rest but augments its utilization during subsequent exercise
Shiou-Liang Wee,1 Clyde Williams,1 Kostas Tsintzas,2 and Leslie Boobis3
1Sports and Exercise Nutrition Research Group, School of Sport and Exercise Sciences, Loughborough University, Loughborough; 2Centre for Integrated Systems Biology and Medicine, School of Biomedical Sciences, Nottingham University, Nottingham; and 3Sunderland Royal Hospital, Sunderland, United Kingdom
Submitted 8 November 2004 ; accepted in final form 12 April 2005
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.
In summary, our findings indicate that:
1) a HGI meal results in greater muscle glycogen storage than a LGI meal in overnight fasted subjects with normal glycogen concentration;
2) the relative shift in substrate metabolism during 30 min of exercise from CHO to fat after ingestion of a LGI compared with a HGI meal was accompanied by a reduction in the rate of muscle glycogen utilization and not blood glucose oxidation; and
3) compared with MG, concentrations of PG appear to be more sensitive to feeding and exercise when total glycogen is not supercompensated or depleted.
However, the greater fat oxidation and lower muscle glycogen utilization after the LGI meal may not always translate to a greater endurance capacity than after the HGI meal, as indicated by the inconsistency in the literature regarding the ergogenic effects of LGI or MGI meals over high GI meals. Further studies are required to investigate the relative roles of muscle and liver glycogen in energy metabolism and the onset of fatigue during exercise performed after ingestion of meals with different glycemic indexes.
FONTE: http://jap.physiology.org/content/99/2/707.full.pdf+html
in allegato c'è lo studio completo
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