Effects of fat adaptation and carbohydrate restoration on prolonged endurance exercise.
We determined the effect of fat adaptation on metabolism and performance during 5 h of cycling in seven competitive athletes who consumed a standard carbohydrate (CHO) diet for 1 day and then either a high-CHO diet (11 g. kg(-1)x day(-1) CHO, 1 g x kg(-1) x day(-1) fat; HCHO) or an isoenergetic high-fat diet (2.6 g x kg(-1) x day(-1) CHO, 4.6 g x kg(-1) x day(-1) fat; fat-adapt) for 6 days. On day 8, subjects consumed a high-CHO diet and rested. On day 9, subjects consumed a preexercise meal and then cycled for 4 h at 65% peak O(2) uptake, followed by a 1-h time trial (TT). Compared with baseline, 6 days of fat-adapt reduced respiratory exchange ratio (RER) with cycling at 65% peak O(2) uptake [0.78 +/- 0.01 (SE) vs. 0.85 +/- 0.02; P < 0.05]. However, RER was restored by 1 day of high-CHO diet, preexercise meal, and CHO ingestion (0.88 +/- 0.01; P < 0.05). RER was higher after HCHO than fat-adapt (0.85 +/- 0.01, 0.89 +/- 0.01, and 0.93 +/- 0.01 for days 2, 8, and 9, respectively; P < 0.05). Fat oxidation during the 4-h ride was greater (171 +/- 32 vs. 119 +/- 38 g; P < 0.05) and CHO oxidation lower (597 +/- 41 vs. 719 +/- 46 g; P < 0.05) after fat-adapt. Power output was 11% higher during the TT after fat-adapt than after HCHO (312 +/- 15 vs. 279 +/- 20 W; P = 0.11). In conclusion, compared with a high-CHO diet, fat oxidation during exercise increased after fat-adapt and remained elevated above baseline even after 1 day of a high-CHO diet and increased CHO availability. However, this study failed to detect a significant benefit of fat adaptation to performance of a 1-h TT undertaken after 4 h of cycling.
Carey
A L
AL
Exercise Metabolism Group, Department of Human Biology and Movement Science, RMIT University, Bundoora, Victoria 3083, Australia.
Staudacher
H M
HM
Cummings
N K
NK
Stepto
N K
NK
Nikolopoulos
V
V
Burke
L M
LM
Hawley
J A
JA
D000222:Adaptation, Physiological; D000328:Adult; D001642:Bicycling; D001769:Blood / Q000378:metabolism; D001786:Blood Glucose / Q000378:metabolism; D003187:Compliance; D004032:Diet; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000494:pharmacology*; D004041:Dietary Fats / Q000378:metabolism / Q000494:pharmacology*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008297:Male; D010084:Oxidation-Reduction; D010806:Physical Education and Training; D010807:Physical Endurance / Q000187:drug effects*; D013997:Time Factors
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D004041:Dietary Fats