Enough energy, available carbohydrate and better performance

Two questions about fuel

A person can consume too little total energy for their activity, too little carbohydrate for a particular exercise demand, or both. These exposures should be measured separately. EPK combines an estimate of daily energy needs with a high-carbohydrate, low-fat dietary approach; research must establish what each component contributes.

What low energy availability did in a controlled experiment

Jeppesen and colleagues studied 12 female endurance athletes in a randomised crossover trial. Each completed 14 days at approximately 22 or 52 kcal/kg fat-free mass/day of energy availability, with training maintained. Low availability increased systemic cortisol by 22% and impaired both a 20-minute cycling time trial and a high-intensity time-to-exhaustion test. Time-trial impairment remained after three days of refuelling. [1]

Energy availability means dietary energy remaining after exercise expenditure, divided by fat-free mass. It is not total intake divided by body weight and is not interchangeable with EPK. These results concern a short, substantial reduction in availability in trained women; they do not identify a universal intake threshold.

More fat oxidation did not mean better racing

Burke and colleagues compared high, periodised and very low carbohydrate availability during intensified training in elite race walkers. The ketogenic low-carbohydrate, high-fat approach increased fat oxidation but impaired exercise economy and negated the performance benefit observed with carbohydrate-supported training. The dietary groups were not randomly allocated, which limits causal interpretation. [2]

The performance problem was relevant to the oxygen cost of maintaining demanding race speeds. Increased capacity to burn fat is therefore not sufficient evidence of an improved ability to perform. The findings do not establish that one carbohydrate intake is optimal for every sport, intensity or person.

Restoring sufficiency and adding a surplus are different interventions

The athlete evidence supports avoiding under-fuelling and supplying carbohydrate for demanding exercise. It does not demonstrate that everyone requires 15% above total daily expenditure for growth or performance improvement. EPK’s approximate 15% performance pathway is a proposed starting strategy requiring evaluation, rather than a threshold established by these experiments.

Wearable expenditure is also an estimate. Eating 15% above a device estimate is not necessarily a measured 15% physiological surplus. Studies of the pathway should document actual intake, training demand, device data, body composition and performance over time.

What an EPK performance trial should measure

A useful comparison would distinguish restoration to estimated energy balance from an additional surplus, while recording carbohydrate in grams per kilogram and keeping protein intake and training comparable. Outcomes should include exercise performance, recovery, hunger, menstrual function where relevant, and changes in fat and lean tissue.

This connects EPK–003’s substrate-utilisation questions with EPK–004’s functional outcomes. Improved performance would be the outcome to demonstrate; neither a higher energy target nor greater fat oxidation should be treated as proof of success.

Related working papers

Read the relevant PDFs: EPK–001 to 007 are the revised version 1.2 papers; EPK–008 to 010 are version 1.0 supplements. Earlier PDFs and DOI records remain on the paper archive.