High fat diet improves metabolic flexibility during progressive exercise to exhaustion (VO 2 max testing) and during 5km running time trials

Athletes on a low-carbohydrate, high-fat diet derived 50% or more of their energy from fat during high-intensity exercise.

• The low-carbohydrate, high-fat diet increased fat oxidation and decreased carbohydrate oxidation without impairing performance in tests to exhaustion or 5km runs.
• Following the low-carbohydrate, high-fat diet, athletes reached a point where fat provided most of their energy at exercise intensities up to 90% VOmax.
• In contrast, the high-carbohydrate, low-fat diet resulted in carbohydrate supplying more than 50% of energy across all exercise intensities.
• During the 5km time trial, energy from fat accounted for approximately 56% after the low-carbohydrate diet, while over 93% was derived from carbohydrate after the high-carbohydrate diet.
• These findings suggest greater metabolic flexibility with low-carbohydrate, high-fat eating and challenge the belief in carbohydrate dependence for high-intensity exercise.

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