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


METHODS
Eight well-trained subjects consumed either a high-CHO (9.3 g x kg(-1) x d(-1) CHO, 1.1 g x kg(-1) x d(-1) fat; HCHO) or an isoenergetic high-fat diet (2.5 g x kg(-1) x d(-1) CHO, 4.3 g x kg(-1) x 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 O(2) uptake [VO(2peak)] + time trial [TT]) of 7 kJ x kg(-1)) was undertaken after a CHO breakfast (CHO 2 g x kg(-1)) and intake of CHO during cycling (0.8 g x kg(-1) x h(-1)).


RESULTS
FAT-adapt reduced respiratory exchange ratio (RER) values before and during cycling at 70% VO(2peak); 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).


CONCLUSIONS
Adaptations 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 approximately 25 min undertaken after 2 h of submaximal cycling.
Burke
Louise M
LM
Sports Science and Sports Medicine, Australian Institute of Sport, Belconnen 2616, Australia. louise.burke@ausport.gov.au
Hawley
John A
JA
Angus
Damien J
DJ
Cox
Gregory R
GR
Clark
Sally A
SA
Cummings
Nicola K
NK
Desbrow
Ben
B
Hargreaves
Mark
M
D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D001642:Bicycling / Q000502:physiology*; D001786:Blood Glucose / Q000032:analysis; D018592:Cross-Over Studies; D004040:Dietary Carbohydrates / Q000378:metabolism*; D004041:Dietary Fats / Q000378:metabolism*; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology*; D005215:Fasting / Q000378:metabolism; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005990:Glycerol / Q000097:blood; D006801:Humans; D007328:Insulin / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D008297:Male; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology; D013647:Task Performance and Analysis
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D019344:Lactic Acid; D005990:Glycerol