Muscle glycogen storage after prolonged exercise: effect of the frequency of carbohydrate feedings.
We reported previously that intake of carbohydrate foods with a high glycemic index (GI) produced greater glycogen storage and greater postprandial glucose and insulin responses during 24 h of postexercise recovery than did intake of low-GI carbohydrate foods. In the present study we examined the importance of the greater incremental glucose and insulin concentrations on glycogen repletion by comparing intake of large carbohydrate meals ("gorging") with a pattern of frequent, small, carbohydrate snacks ("nibbling"), which simulates the flattened glucose and insulin responses after low-GI carbohydrate meals. Eight well-trained triathletes [x +/- SEM: 25.6 +/- 1.5 y of age, weighing 70.2 +/- 1.9 kg, and with a maximal oxygen uptake (VO2max) of 4.2 +/- 0.2 L/min] undertook an exercise trial (2 h at 75% VO2max followed by four 30-s sprints) to deplete muscle glycogen on two occasions, 1 wk apart For 24 h after each trial, subjects rested and consumed the same diet composed exclusively of high-GI carbohydrate foods, providing 10 g carbohydrate/kg body mass. The "gorging" trial provided the food as four large meals of equal carbohydrate content eaten at 0, 4, 8, and 20 h of recovery, whereas in the "nibbling" trial each of the meals was divided into four snacks and fed at hourly intervals (0-11, 20-23 h). However, there was no significant difference in muscle glycogen storage between the two groups over the 24 h (gorging: 74.1 +/- 8.0 mmol/kg wet wt; nibbling: 94.5 +/- 14.6 mmol/kg wet wt). The results of this study suggest that there is no difference in postexercise glycogen storage over 24 h when a high-carbohydrate diet is fed as small frequent snacks or as large meals, and that a mechanism other than lowered blood glucose and insulin concentrations needs to be sought to explain the reduced rate of glycogen storage after consumption of low-GI carbohydrate foods.
Burke
L M
LM
Department of Sports Science, Australian Institute of Sport, Canberra, Australia. lburke@ausport.gov.au
Collier
G R
GR
Davis
P G
PG
Fricker
P A
PA
Sanigorski
A J
AJ
Hargreaves
M
M
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D015444:Exercise / Q000502:physiology*; D006003:Glycogen / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood; D009132:Muscles / Q000378:metabolism*; D010101:Oxygen Consumption; D013177:Sports; D013997:Time Factors
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D007328:Insulin; D006003:Glycogen