Keto-adaptation may double exercise fat use to ∼1.5 g min within 3-4 weeks in elite athletes.
A ketogenic low-carbohydrate, high-fat diet significantly enhances muscle .
Fat oxidation rates can shift from approximately 45% to 70% of maximal aerobic capacity during exercise.
There are reciprocal reductions in carbohydrate oxidation, which may impair glycogen use in high-intensity exercise.
Current evidence does not strongly support normalization of muscle glycogen content with long-term adherence to K-LCHF diets.
Individual responses to K-LCHF diets vary widely among endurance athletes.
Periodization of K-LCHF with high carbohydrate availability may not provide benefits over standard sports nutrition guidelines.
Simplified
The ability of ketogenic low-carbohydrate (CHO) high-fat (K-LCHF) diets to enhance muscle has led to claims that it is the 'future of elite endurance sport'. There is robust evidence that substantial increases in fat oxidation occur, even in elite athletes, within 3-4 weeks and possibly 5-10 days of adherence to a K-LCHF diet. Retooling of the muscle can double exercise fat use to ∼1.5 g min, with the intensity of maximal rates of oxidation shifting from ∼45% to ∼70% of maximal aerobic capacity. Reciprocal reductions in CHO oxidation during exercise are clear, but current evidence to support the hypothesis of the normalization of muscle glycogen content with longer-term adaptation is weak. Importantly, keto-adaptation may impair the muscle's ability to use glycogen for oxidative fates, compromising the use of a more economical energy source when the oxygen supply becomes limiting and, thus, the performance of higher-intensity exercise (>80% maximal aerobic capacity). Even with moderate intensity exercise, individual responsiveness to K-LCHF is varied, with extremes at both ends of the performance spectrum. Periodisation of K-LCHF with high CHO availability might offer opportunities to restore capacity for higher-intensity exercise, but investigations of various models have failed to find a benefit over dietary approaches based on current sports nutrition guidelines. Endurance athletes who are contemplating the use of K-LCHF should undertake an audit of event characteristics and personal experiences to balance the risk of impaired performance of higher-intensity exercise with the likelihood of an unavoidable depletion of carbohydrate stores. -1
Key numbers
1.5 g min
Increase in Rate
Maximal rate achieved after K-LCHF adaptation.
−1.6%
Performance Change in 10,000 m Race
K-LCHF group showed a decrease in race performance compared to HCHO.
6.6%
Improvement in HCHO Group
HCHO group improved significantly in the same race.
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