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Low carbohydrate high fat ketogenic diets on the exercise crossover point and glucose homeostasis.
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- Author(s): Noakes, T. D.; Prins, P. J.; Volek, J. S.; D'Agostino, D. P.; Koutnik, A. P.
- Source:
Frontiers in Physiology; 3/28/2023, Vol. 14, p1-14, 14p- Subject Terms:
- Source:
- Additional Information
- Abstract: In exercise science, the crossover effect denotes that fat oxidation is the primary fuel at rest and during low-intensity exercise with a shift towards an increased reliance on carbohydrate oxidation at moderate to high exercise intensities. This model makes four predictions: First, >50% of energy comes from carbohydrate oxidation at ≥60% of maximum oxygen consumption (VO
2 max), termed the crossover point. Second, each individual has a maximum fat oxidation capacity (FATMAX) at an exercise intensity lower than the crossover point. FATMAX values are typically 0.3-0.6 g/min. Third, fat oxidation is minimized during exercise ≥85% VO2 max, making carbohydrates the predominant energetic substrate during highintensity exercise, especially at >85%VO2 max. Fourth, high-carbohydrate low-fat (HCLF) diets will produce superior exercise performances via maximizing preexercise storage of this predominant exercise substrate. In a series of recent publications evaluating the metabolic and performance effects of lowcarbohydrate high-fat (LCHF/ketogenic) diet adaptations during exercise of different intensities, we provide findings that challenge this model and these four predictions. First, we show that adaptation to the LCHF diet shifts the crossover point to a higher %VO2 max (>80%VO2 max) than previously reported. Second, substantially higher FATMAX values (>1.5 g/min) can be measured in athletes adapted to the LCHF diet. Third, endurance athletes exercising at >85%VO2 max, whilst performing 6 × 800m running intervals, measured the highest rates of fat oxidation yet reported in humans. Peak fat oxidation rates measured at 86.4 ± 6.2%VO2 max were 1.58 ± 0.33 g/min with 30% of subjects achieving >1.85 g/min. These studies challenge the prevailing doctrine that carbohydrates are the predominant oxidized fuel during high-intensity exercise. We recently found that 30% of middle-aged competitive athletes presented with pre-diabetic glycemic values while on an HCLF diet, which was reversed on LCHF. We speculate that these rapid changes between diet, insulin, glucose homeostasis, and fat oxidation might be linked by diet-induced changes in mitochondrial function and insulin action. Together, we demonstrate evidence that challenges the current crossover concept and demonstrate evidence that a LCHF diet may also reverse features of pre-diabetes and future metabolic disease risk, demonstrating the impact of dietary choice has extended beyond physical performance even in athletic populations. [ABSTRACT FROM AUTHOR] - Abstract: Copyright of Frontiers in Physiology is the property of Frontiers Media S.A. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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