Research
Macro partitioning
Endurance training increases absolute rates of fat oxidation but does not change the relative balance of substrate utilization (CHO vs. fat) when exercise is performed at the same relative intensity (percentage of VO2max).
Endurance training makes you faster and allows you to burn more fat in absolute terms, but your body still relies primarily on carbohydrates for energy at any given percentage of your maximum effort. Do not expect training alone to make you a 'fat-burning machine' at high intensities.
StrongQualifiesHIGH confidence
when tested at the same relative intensity (65 % of pre- and post-training VO2max), RER values (0.95), leg RQ (0.98), net FFA uptake and muscle TG utilization were not different... these data demonstrate that the balance of substrate utilization was unaffected by prior endurance training and that CHO-derived energy sources are the major fuel source for working muscle even during 1 h of moderate-intensity exercise.
Why this rating
Based on multiple studies using direct biopsy and isotopic tracer techniques in trained subjects.
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
Related findings · Macro partitioning
- Total daily protein intake of 1.6 g/kg/day is sufficient for maximizing resistance training-induced muscle gains, with an upper confidence interval of 2.2 g/kg/day.Strong
- Resistance exercise training combined with sufficient dietary protein intake acts synergistically to maximize skeletal muscle hypertrophy, with protein intake saturating around 1.6 g/kg/day for general populations and potentially requiring 2.0-2.2 g/kg/day for resistance-trained individuals.Strong
- Trans fats should be completely eliminated from the diet, as they increase LDL cholesterol, decrease HDL cholesterol, and are directly associated with increased coronary risk.Strong
This is one finding among thousands. Every one is graded and traced to its source, so you can see what the evidence actually supports. Browse the research →