The Claim
Ultra-endurance runners on a long-term low-carbohydrate diet achieve peak fat oxidation at a higher percentage of VO2max (70.3%) than those on a high-carbohydrate diet (54.9%), demonstrating a shift in the exercise intensity at which fat becomes the dominant fuel source.
What the research says
Supports is higher
Support is ahead, but a single strong opposing study can change this.
These are independent scores, not a percentage. Higher-grade studies count more, so a single strong opposing study can outweigh several weaker ones.
Ultra-endurance runners who eat a low-carbohydrate diet for a long time reach their highest rate of fat burning at 70.3% of their maximum oxygen uptake, while those on a high-carbohydrate diet reach it at 54.9%.
See the scientific wording
Ultra-endurance runners on a long-term low-carbohydrate diet achieve peak fat oxidation at a higher percentage of VO2max (70.3%) compared to those on a high-carbohydrate diet (54.9%), indicating a shift in the intensity at which fat becomes the dominant fuel source during exercise.
When a person eats very little carbohydrate for a long time, their muscles learn to burn fat more efficiently even during intense exercise. This happens because their muscle cells make more structures that pull fat into energy factories, increase the number of those factories, and turn off the switch that normally favors burning sugar. As a result, fat becomes the main fuel at higher exercise levels than normal.
What the research says
1 studyStudy: Metabolic characteristics of keto-adapted ultra-endurance runners.
Runners who eat mostly fat and very few carbs can burn fat as their main fuel even when running much harder than runners who eat lots of carbs. Their bodies adapt to use fat more efficiently at high intensities.
Score breakdown, mechanism chain, raw evidence, ideal studies needed & 1 supporting studies
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.