Ketone Diester Ingestion Impairs Time-Trial Performance in Professional Cyclists.
Level 2 - randomized trial
Randomized crossover trial
PubMed 29109686 · doi:10.3389/fphys.2017.00806
What was done
Ten elite male cyclists completed a simulated ~31 km laboratory cycling time trial (~50 minutes) in a randomized crossover study. Participants consumed a standardized high-carbohydrate dinner (2 g/kg body mass) and breakfast (2 g/kg carbohydrate plus 200 mg caffeine) before trial days. Cyclists were randomized to consume either a 1,3-butanediol acetoacetate diester (2 × 250 mg/kg) or a placebo drink ~30 minutes before and immediately prior to a 20-minute incremental warm-up. Blood and urine samples were collected before, during, and after the warm-up and time trial to assess ketone concentrations and substrate metabolism.
What was found
Pre-exercise ingestion of the ketone diester resulted in a 2 ± 1% impairment in cycling time-trial performance compared to placebo. This performance decrease was associated with gut discomfort and a higher perception of effort. Serum β-hydroxybutyrate, serum acetoacetate, and urine ketone concentrations increased from rest after ketone ingestion and remained higher than placebo throughout the trial. Absolute values for ketone concentrations and completion times were not reported in the abstract.
Why it matters
Exogenous ketones are frequently promoted as ergogenic aids for endurance performance. This study demonstrates that ketone diester ingestion in carbohydrate-fed elite cyclists impairs short-duration time-trial performance, largely driven by gastrointestinal distress.
Limits
The study sample was small (n = 10) and restricted to elite male cyclists, limiting generalizability to females and non-elite athletes. The results apply specifically to a 1,3-butanediol acetoacetate diester formulation and cannot be generalized to other ketone supplements, such as ketone monoesters or ketone salts. The abstract does not provide exact numerical values for ketone concentrations, time splits, or gastrointestinal symptom scores.
Cited by
- supports 1,3-butanediol acetoacetate diester elevates blood levels of beta-hydroxybutyrate and acetoacetate in approximately a one-to-one ratio.