Macro partitioning
Brief adaptation (5-6 days) to a ketogenic low-carbohydrate high-fat (LCHF) diet impairs high-intensity endurance performance and increases the oxygen cost of exercise, even when muscle glycogen is acutely restored prior to competition.
If you are an endurance athlete, switching to a very low-carb, high-fat diet for even a few days can hurt your race performance, even if you eat a lot of carbs right before the event. Your body's ability to use carbs efficiently at high intensities takes longer than 24 hours to recover. Stick to high-carbohydrate availability for key workouts and races to maintain speed and efficiency.
Acute restoration of CHO availability failed to overturn the impairment of high-intensity endurance performance previously associated with low carbohydrate high fat adaptation, potentially due to the blunted capacity for CHO oxidation.
Why this rating
Randomized controlled trial with elite athletes, rigorous metabolic measurements, and clear performance outcomes, though sample size is small (n=13).
Source
Adaptation to a low carbohydrate high fat diet is rapid but impairs endurance exercise metabolism and performance despite enhanced glycogen availability
Louise M. Burke et al. · The Journal of Physiology · 2020
DOI 10.1113/jp280221
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