Biology of Sport
eISSN: 2083-1862
ISSN: 0860-021X
Biology of Sport
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SCImago Journal & Country Rank
2/2023
vol. 40
 
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abstract:
Original paper

High fat diet improves metabolic flexibility during progressive exercise to exhaustion (VO2max testing) and during 5km running time trials

Philip J. Prins
1
,
Timothy D. Noakes
2
,
Jeffrey D. Buxton
2
,
Gary L. Welton
2
,
Amy S. Raabe
3
,
Katie E. Scott
2
,
Adam D. Atwell
2
,
Sarah J. Haley
2
,
Noah J. Esbenshade
2
,
Jacqueline Abraham
2

1.
Grove City College, Grove City, PA, USA
2.
Department of Medical and Wellness Science, Cape Peninsula University of Technology, Cape Town, South Africa
3.
Youngstown State University, Youngstown, OH, USA
Biol Sport.2023;40(2):465–475
Online publish date: 2022/07/19
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Recently we reported similar performances in both progressive tests to exhaustion (VO2max) and 5km running time trials (5KTT) after consuming low-carbohydrate, high-fat (LCHF) or high-carbohydrate, low-fat (HCLF) diets. Accordingly, we tested the null hypothesis that the metabolic responses during both tests would be similar across diets. In a randomized, counterbalanced, cross-over design, seven male athletes (VO2max: 61.9 ± 6.1 mL/kg/min; age: 35.6 ± 8.4 years; height: 178.7 ± 4.1 cm; mass: 68.6 ± 1.6 kg; body fat: 5.0 ± 1.3%) completed six weeks of LCHF (6/69/25% energy carbohydrate/fat/protein) and HCLF (57/28/15% energy carbohydrate/fat/protein) diets, separated by a two-week washout. Substrate utilization and energy expenditure were measured during VO2max tests and 5KTTs. The LCHF diet markedly increased fat oxidation and reduced carbohydrate oxidation, with no associated impairment in either the VO2max tests or the 5KTTs. Following the LCHF diet, athletes generated 50% or more of their energy requirements from fat at exercise intensities up to 90% VO2max and reached the crossover point for substrate utilization at ~85% VO2max. In contrast, following the HCLF diet, carbohydrate provided more than 50% of the total energy consumption at all exercise intensities. During the 5KTT, ~56% of energy was derived from fat following the LCHF diet whereas more than 93% of the energy came from carbohydrate following the HCLF diet. This study provides evidence of greater metabolic flexibility following LCHF eating and challenges the popular doctrines of “carbohydrate dependence” for high intensity exercise and the role dietary macronutrients play in human performance.
keywords:

crossover point, high fat diet, low-carbohydrate, high-carbohydrate, fat oxidation, carbohydrate oxidation

 
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