Research
Macro partitioning
Increasing relative exercise intensity shifts fuel utilization from fat to carbohydrate, with carbohydrate becoming the predominant fuel source above the 'crossover point' (typically ~50% VO2max in untrained individuals).
As you exercise harder (higher % of your max capacity), your body switches from burning fat to burning sugar. For fat loss purposes, moderate intensity allows for higher fat oxidation, but high intensity burns more total calories and sugar.
StrongSupportsVERY_HIGH confidence
As relative exercise intensity is increased, there is a decrease in the proportion of the energy requirement derived from fat oxidation and an increase in that provided by carbohydrate oxidation.
Why this rating
Supported by extensive data and figures in the review.
Source
The regulation of carbohydrate and fat metabolism during and after exercise
John O. Holloszy · Frontiers in bioscience · 1998
DOI 10.2741/a342
narrative_reviewCited 177×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
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