Research
Macro partitioning
High-fat, low-carbohydrate diets impair high-intensity endurance performance by down-regulating pyruvate dehydrogenase (PDH) activity and reducing muscle glycogenolysis rates, thereby limiting ATP production at intensities above 60% VO2max.
If you train or race at high intensities (above 60% of your max effort), avoid high-fat, low-carb diets. They slow down your body's ability to use carbohydrates, which are your primary fuel for speed. Stick to high-carbohydrate availability to maintain performance.
StrongRefutesHIGH confidence
fat-rich diets do not 'spare' CHO (i.e., muscle glycogen) or improve training capacity/performance but, instead, directly impair rates of muscle glycogenolysis and energy flux. This down-regulation of CHO metabolism underpins the reductions in high-intensity exercise capacity observed after high-fat feeding.
Why this rating
Based on a comprehensive review of multiple studies using direct biopsy measures, isotopic tracers, and enzyme activity assays in trained athletes.
Source
Carbohydrate Dependence During Prolonged, Intense Endurance Exercise
John A. Hawley et al. · Sports Medicine · 2015
DOI 10.1007/s40279-015-0400-1
narrative_reviewCited 166×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
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