Adaptations to short-term high-fat diet persist during exercise despite high carbohydrate availability

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BURKE, L. M., J. A. HAWLEY, D. J. ANGUS, G. R. COX, S. CLARK, N. K. CUMMINGS, B. DESBROW, and M. HARGREAVES. Adaptations to short-term high-fat diet persist during exercise despite high carbohydrate availability. Med. Sci. Sports Exerc., Vol. 34, No. 1, 2002, pp. 83–91.PurposeFive days of a high-fat diet produce metabolic adaptations that increase the rate of fat oxidation during prolonged exercise. We investigated whether enhanced rates of fat oxidation during submaximal exercise after 5 d of a high-fat diet would persist in the face of increased carbohydrate (CHO) availability before and during exercise.MethodsEight well-trained subjects consumed either a high-CHO (9.3 g·kg−1·d−1 CHO, 1.1 g·kg−1·d−1 fat; HCHO) or an isoenergetic high-fat diet (2.5 g·kg−1·d−1 CHO, 4.3 g·kg−1·d−1 fat; FAT-adapt) for 5 d followed by a high-CHO diet and rest on day 6. On day 7, performance testing (2 h steady-state (SS) cycling at 70% peak O2 uptake [V̇O2peak] + time trial [TT]) of 7 kJ·kg−1) was undertaken after a CHO breakfast (CHO 2 g·kg−1) and intake of CHO during cycling (0.8 g·kg−1·h−1).ResultsFAT-adapt reduced respiratory exchange ratio (RER) values before and during cycling at 70% V̇O2peak; RER was restored by 1 d CHO and CHO intake during cycling (0.90 ± 0.01, 0.80 ± 0.01, 0.91 ± 0.01, for days 1, 6, and 7, respectively). RER values were higher with HCHO (0.90 ± 0.01, 0.88 ± 0.01 (HCHO > FAT-adapt, P < 0.05), 0.95 ± 0.01 (HCHO > FAT-adapt, P < 0.05)). On day 7, fat oxidation remained elevated (73 ± 4 g vs 45 ± 3 g, P < 0.05), whereas CHO oxidation was reduced (354 ± 11 g vs 419 ± 13 g, P < 0.05) throughout SS in FAT-adapt versus HCHO. TT performance was similar for both trials (25.53 ± 0.67 min vs 25.45 ± 0.96 min, NS).ConclusionAdaptations to a short-term high-fat diet persisted in the face of high CHO availability before and during exercise, but failed to confer a performance advantage during a TT lasting ∼ 25 min undertaken after 2 h of submaximal cycling.

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