Ketone Diester Ingestion Impairs Time-Trial Performance in Professional Cyclists

We investigated the effect of pre- race ingestion of a 1,3-butanediol acetoacetate diester on blood ketone concentration, substrate metabolism and performance of a cycling time trial (TT) in professional cyclists. In a randomized cross-over design, 10 elite male cyclists completed a similar to 31 km laboratory-based TT on a cycling ergometer programmed to simulate the 2017 World Road Cycling Championships course. Cyclists consumed a standardizedmeal [2 g/kg bodymass (BM) carbohydrate (CHO)] the evening prior to a trial day and a CHO breakfast (2 g/kg BM CHO) with 200 mg caffeine on the morning of a trial day. Cyclists were randomized to consume either the ketone diester (2 x 250 mg/kg) or a placebo drink, followed immediately by 200mL diet cola, given similar to 30min before and immediately prior to commencing a 20min incremental warm-up. Blood samples were collected prior to and during the warm-up, pre- and post-TT and at regular intervals after the TT. Urine samples were collected pre-and post-warm-up, immediately post TT and 60min post TT. Pre-exercise ingestion of the diester resulted in a 2 +/- 1% impairment in TT performance that was associated with gut discomfort and higher perception of effort. Serum beta-hydroxybutyrate, serum acetoacetate, and urine ketone concentrations increased from rest following ketone ingestion and were higher than placebo throughout the trial. Ketone ingestion induces hyperketonemia in elite professional cyclists when in a carbohydrate fed state, and impairs performance of a cycling TT lasting similar to 50min.