title: Effect of fat adaptation and carbohydrate restoration on metabolism and performance during prolonged cycling.
abstract: For 5 days, eight well-trained cyclists consumed a random order of a high-carbohydrate (CHO) diet (9.6 g. kg(-1). day(-1) CHO, 0.7 g. kg(-1). day(-1) fat; HCHO) or an isoenergetic high-fat diet (2.4 g. kg(-1). day(-1) CHO, 4 g. kg(-1). day(-1) fat; Fat-adapt) while undertaking supervised training. On day 6, subjects ingested high CHO and rested before performance testing on day 7 [2 h cycling at 70% maximal O(2) consumption (SS) + 7 kJ/kg time trial (TT)]. With Fat-adapt, 5 days of high-fat diet reduced respiratory exchange ratio (RER) during cycling at 70% maximal O(2) consumption; this was partially restored by 1 day of high CHO [0.90 +/- 0.01 vs. 0.82 +/- 0.01 (P < 0.05) vs. 0.87 +/- 0.01 (P < 0.05), for day 1, day 6, and day 7, respectively]. Corresponding RER values on HCHO trial were [0. 91 +/- 0.01 vs. 0.88 +/- 0.01 (P < 0.05) vs. 0.93 +/- 0.01 (P < 0.05)]. During SS, estimated fat oxidation increased [94 +/- 6 vs. 61 +/- 5 g (P < 0.05)], whereas CHO oxidation decreased [271 +/- 16 vs. 342 +/- 14 g (P < 0.05)] for Fat-adapt compared with HCHO. Tracer-derived estimates of plasma glucose uptake revealed no differences between treatments, suggesting muscle glycogen sparing accounted for reduced CHO oxidation. Direct assessment of muscle glycogen utilization showed a similar order of sparing (260 +/- 26 vs. 360 +/- 43 mmol/kg dry wt; P = 0.06). TT performance was 30.73 +/- 1.12 vs. 34.17 +/- 2.48 min for Fat-adapt and HCHO (P = 0.21). These data show significant metabolic adaptations with a brief period of high-fat intake, which persist even after restoration of CHO availability. However, there was no evidence of a clear benefit of fat adaptation to cycling performance.
authors.affiliation: Sports Science and Sports Medicine, Australian Institute of Sport, Belconnen 2616, Australia. louise.burke@ausport.gov.au
authors.forename: L M
authors.initials: LM
authors.lastname: Burke
authors.forename: D J
authors.initials: DJ
authors.lastname: Angus
authors.forename: G R
authors.initials: GR
authors.lastname: Cox
authors.forename: N K
authors.initials: NK
authors.lastname: Cummings
authors.forename: M A
authors.initials: MA
authors.lastname: Febbraio
authors.forename: K
authors.initials: K
authors.lastname: Gawthorn
authors.forename: J A
authors.initials: JA
authors.lastname: Hawley
authors.forename: M
authors.initials: M
authors.lastname: Minehan
authors.forename: D T
authors.initials: DT
authors.lastname: Martin
authors.forename: M
authors.initials: M
authors.lastname: Hargreaves
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001642:Bicycling / Q000502:physiology*; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D004041:Dietary Fats / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D008297:Male; D008660:Metabolism / Q000187:drug effects; D018482:Muscle, Skeletal / Q000378:metabolism; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D011659:Pulmonary Gas Exchange / Q000187:drug effects; D011897:Random Allocation; D013997:Time Factors
chemical_list: D004040:Dietary Carbohydrates; D004041:Dietary Fats; D006003:Glycogen