Effect of fat adaptation and carbohydrate restoration on metabolism and performance during prolonged cycling

Louise M. Burke*, Damien J. Angus, Gregory R. Cox, Nicola K. Cummings, Mark A. Febbraio, Kathryn Gawthorn, John A. Hawley, Michelle Minehan, David T. Martin, Mark Hargreaves

*Corresponding author for this work

Research output: Contribution to journalArticleResearchpeer-review

140 Citations (Scopus)

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↑ 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 O2 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 O2 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.

Original languageEnglish
Pages (from-to)2413-2421
Number of pages9
JournalJournal of Applied Physiology
Volume89
Issue number6
DOIs
Publication statusPublished - 2000
Externally publishedYes

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