Post-Exercise R-1,3-Butanediol did not Improve Markers of Fatigue or Recovery During a Multi-Stage Mountain Bike Race.

Evidence suggests that exogenous ketosis (EK) induced by ketone monoester (KME) supports recovery and attenuates physiological stress during endurance exercise. However, the potential benefits of the ketone precursor R-1,3-butanediol (BDO) during real-world multi-stage cycling remain unknown. We investigated the effects of post-exercise BDO supplementation on physiological strain, dietary intake, hydration, cognitive function, sleep, and subjective recovery during the 2025 Absa Cape Epic mountain bike race. In this double-blind, placebo-controlled study, 18 trained mountain bikers (10 teams) completed an 8-day multi-stage race. Participants received either 87.5 mL ketone IQ (BDO) or a placebo (CON) twice daily (post-stage and pre-sleep). Heart rate, energy intake, sleep metrics, cognitive performance, and subjective stress-recovery were monitored throughout the race. BDO induced mild post-stage ketosis (∼1.0 mM β-hydroxybutyrate) from stage 1 onwards. Across the race, both groups demonstrated lower exercise heart rate, increased resting heart rate, increased energy and carbohydrate intake, and slower reaction time by stage 6, indicating accumulating physiological strain. BDO did not alter any of these effects compared with placebo. These findings suggest that the modest ketosis achieved with BDO was not effective under real-world racing conditions, highlighting the importance of formulation-specific and ecologically valid evaluations of exogenous ketosis strategies in future studies.