Effect of a four-week isocaloric ketogenic diet on physical performance at very high-altitude: a pilot study

A ketogenic diet (KD) reduces daily carbohydrates (CHOs) ingestion by replacing most calories with fat. KD is of increasing interest among athletes because it may increase their maximal oxygen uptake (VO₂max), the principal performance limitation at high-altitudes (1500-3500 m). We examined the tolerance of a 4-week isocaloric KD (ICKD) under simulated hypoxia and the possibility of evaluating ICKD performance benefits with a maximal graded exercise bike test under hypoxia and collected data on the effect of the diet on performance markers and arterial blood gases.

In a randomised single-blind cross-over model, 6 recreational mountaineers (age 24-44 years) completed a 4-week ICKD followed or preceded by a 4-week usual mixed Western-style diet (UD). Performance parameters (VO₂max, lactate threshold [LT], peak power [P_peak]) and arterial blood gases (PaO₂, PaCO₂, pH, HCO₃^-) were measured at baseline under two conditions (normoxia and hypoxia) as well as after a 4-week UD and 4-week ICKD under the hypoxic condition.

We analysed data for all 6 participants (BMI 19.9-24.6 kg m^-2). Mean VO₂max in the normoxic condition was 44.6 ml kg^-1 min^-1. Hypoxia led to decreased performance in all participants. With the ICKD diet, median values for PaO₂ decreased by - 14.5% and VO₂max by + 7.3% and P_peak by + 4.7%.

All participants except one could complete the ICKD. VO₂max improved with the ICKD under the hypoxia condition. Therefore, an ICKD is an interesting alternative to CHOs dependency for endurance performance at high-altitudes, including high-altitude training and high-altitude races. Nevertheless, decreased PaO₂ with ICKD remains a significant limitation in very-high to extreme altitudes (> 3500 m). Trial registration Clinical trial registration Nr. NCT05603689 (Clinicaltrials.gov). Ethics approval CER-VD, trial Nr. 2020-00427, registered 18.08.2020-prospectively registered.