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

BACKGROUND: 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 (VO(2)max), 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. METHODS: 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 (VO(2)max, lactate threshold [LT], peak power [P(peak)]) and arterial blood gases (PaO(2), PaCO(2), pH, HCO(3)(−)) 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. RESULTS: We analysed data for all 6 participants (BMI 19.9–24.6 kg m(−2)). Mean VO(2)max 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 PaO(2) decreased by − 14.5% and VO(2)max by + 7.3% and P(peak) by + 4.7%. CONCLUSION: All participants except one could complete the ICKD. VO(2)max 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 PaO(2) 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.