ABSTRACT
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 (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. 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 (VO2max, lactate threshold [LT], peak power [Ppeak]) 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. RESULTS: 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 Ppeak by + 4.7%. CONCLUSION: 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.
ABSTRACT
More and more travelers are exposed to high altitude, for example, 176'000 trekkers/climbers were registered in Nepal in 2017. Individual predispositions, a history of altitude illness, the existence of risk factors and/or comorbidities increase the risk of developing specific altitude-related diseases that are potentially life threatening. Nevertheless, the prediction of these diseases remains difficult, especially in subjects without prior exposure to high altitude. In this context different altitude simulation tests have been developed. Their indication, practice and validity are summarized in this article.
De plus en plus de voyageurs s'exposent à la haute altitude, par exemple 176â 000 trekkers/alpinistes ont été enregistrés au Népal en 2017. Des prédispositions individuelles, des antécédents de maladies d'altitude, l'existence de facteurs de risque et/ou comorbidités augmentent le risque de développer des maladies spécifiques liées à l'altitude qui sont potentiellement mortelles. Néanmoins, la prédiction de ces maladies reste difficile, notamment chez des sujets sans exposition préalable à la haute altitude. Dans ce contexte, différents tests de simulation à l'altitude ont été développés. Leurs indication, pratique et validité sont résumées dans cet article.
