Low-carb performance and resting metabolism need separate tests

A performance effect under specific conditions

In a crossover study of 16 exercise-trained adults, four days of ketogenic eating reduced anaerobic cycling power and intermittent-running performance compared with a high-carbohydrate phase with similar reported energy intake [1]. This is relevant to carbohydrate-dependent activity, but the brief adaptation period limits conclusions about long-term performance.

Resting expenditure does not show a uniform decline

A small crossover trial in six endurance athletes found no significant fasting energy-expenditure difference after 14-day ketogenic and high-carbohydrate phases [2]. The study is too small to demonstrate equivalence, but its result does not support a consistent fall in resting expenditure.

In 17 men studied on metabolic wards, switching to an isocaloric ketogenic diet produced small increases in chamber and sleeping expenditure, without faster body-fat loss [3]. Fixed diet order and ongoing weight loss complicate interpretation. Sleeping expenditure is also not identical to a standard RMR assessment.

Define metabolic decline before looking for it

Possible outcomes include reduced RMR after body-composition adjustment, poorer exercise economy, lower peak power, impaired glucose handling or reduced tissue respiration. These outcomes are not interchangeable. Higher fat oxidation alone cannot decide whether function improved.

Papers 3 and 4 should distinguish substrate selection from capacity and performance. A study relevant to Papers 1 and 5 would separately measure calorie intake, carbohydrate availability, protein, activity and adaptation time. That permits testing whether effects relate to low energy intake, low carbohydrate availability or their combination.

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.