THE INFLUENCE OF DIETARY COMPOSITION ON SHORT-TERM AEROBIC TRAINING-INDUCED ADAPTATIONS OF GLUCOSE KINETICS:

The purpose of this study was to examine the influences of dietary composition on short-term aerobic training-induced adaptations of whole body carbohydrate and fat oxidation, glucose kinetics, and exercise performance. Eight healthy, sedentary males (27.2 ± 2 yr, 77.9 ± 2.8 kg, mean ± SE) with a peak oxygen consumption (VO2 peak) of 45.2 ± 2.3 ml·kg−1 ·min−1 underwent two 10 d experimental phases separated by a two-week washout period. During the first 10 d phase subjects were randomly assigned to consume either a high carbohydrate (∼ 7 g carbohydrate ·kg−1 ·d−1) or high fat diet (∼ 3 g carbohydrate · kg−1 ·d−1) while remaining sedentary (CHO or FAT). During the second 10 d phase subjects consumed the opposite diet and both groups performed identical daily aerobic training (CHO + T or FAT + T). CHO did not affect the pattern of whole body substrate oxidation or glucose kinetics during 90 min of moderate intensity (∼54% VO2 peak) exercise. FAT increased whole body fat oxidation at the end of exercise (FATpre: 9.6 ± 2.5; FATpost: 15.7 ± 2.4 μmol · kg−1 · min−1) and reduced glucose rate of appearance (Ra) and disappearance (Rd) at the end of exercise. CHO + T did not greatly alter whole body substrate oxidation during exercise. FAT + T substantially increased whole body fat oxidation throughout exercise (FAT + Tpre: 11.6 ± 1.9; FATpost: 19.5 ± 3.9 · mol ·kg−1 · min−1). Both CHO + T and FAT + T reduced glucose Ra at the end of exercise, while only FAT + T reduced glucose Rd at the end of exercise. There were similar improvements (∼ 11%) in time trial performance for both groups. Thus, high carbohydrate and high fat diets alone do not substantially influence metabolism during exercise, except that high fat diets tend to increase whole body fat oxidation late in prolonged exercise. The increase in whole body fat oxidation late in exercise as the result of a 10 d high fat diet is magnified when accompanied by daily aerobic training for 10 d. High carbohydrate diets consumed during short-term aerobic training eliminate the training-induced increase in whole body fat oxidation. Despite these differences in adaptation of substrate use, CHO + T and FAT + T subjects were equally capable of improving high-intensity time trial performance after 10 d of aerobic training. Supported by the Gatorade Sport Science Institute.