Acute Ketone Monoester Supplementation Impairs 20-min Time-Trial Performance in Trained Cyclists: A Randomized, Crossover Trial

In a randomized, triple-blind, crossover trial, 23 trained cyclists (peak oxygen uptake 65 plus or minus 12 ml per kg per min) ingested 0.35 g/kg body mass of (R)-3-hydroxybutyl (R)-3-hydroxybutyrate ketone ester or a flavor-matched placebo 30 minutes before a 15-minute warm-up and a 20-minute cycling time trial. Preexercise venous beta-hydroxybutyrate was 2.0 plus or minus 0.6 mM after ketone ester versus 0.2 plus or minus 0.1 mM after placebo. Mean time trial power output was 2.4 percent lower after ketone ester than placebo (255 vs 261 W, p < .01). The abstract states that the mechanism behind the impaired performance remains to be determined.