Research
Macro partitioning
Increasing fat availability before exercise (via high-fat diet or fat infusion) reduces carbohydrate utilization but does not improve exercise performance.
Do not rely on high-fat diets or fat infusions to improve your endurance performance. While it changes how your body burns fuel (less carbs, more fat), it does not make you faster and may even make you slower compared to a high-carb diet.
GoodRefutesHIGH confidence
Interventions to increase fat availability before exercise have been shown to reduce carbohydrate utilization during exercise, but do not appear to have ergogenic benefits.
Why this rating
Consistent findings across multiple studies (Starling, Burke, Carey, Hawley) showing no performance benefit.
Source
Pre-exercise carbohydrate and fat ingestion: effects on metabolism and performance
Mark Hargreaves et al. · Journal of Sports Sciences · 2003
DOI 10.1080/0264041031000140536
narrative_reviewCited 178×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
More from this paper
- Ingesting 10–12.5 g carbohydrate per kg body mass per day for 1–7 days prior to competition increases muscle glycogen to 170–180 mmol/kg wet mass and enhances endurance performance in events lasting 90 minutes or more.Good
- Ingesting 200–300 g of carbohydrate 3–4 hours before exercise enhances endurance performance by increasing muscle and liver glycogen and maintaining blood glucose, with effects persisting for up to 6 hours.Good
- Ingesting carbohydrate 30–60 minutes before exercise does not impair performance and may enhance it, despite causing metabolic shifts like increased carbohydrate oxidation and inhibited fat oxidation.Good
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
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