Metabolic characteristics of keto-adapted ultra-endurance runners

In summary, these results provide the first documentation of the metabolic adaptations associated with long-term con- sumption of a very low-carbohydrate/high-fat diet in highly trained keto-adapted ultra-endurance athletes. The enhanced ability to oxidize fat during exercise across a range of intensities is striking, as is the ability to maintain normalglycogen concentrations in the context of limited carbohydrate intake. Keto-adaptation provides an alternative to the supremacy of the high-carbohydrate paradigm for endurance athletes.

https://www.metabolismjournal.com/article/S0026-0495(15)00334-0/fulltext