Exogenous ketosis impacts neither performance nor muscle glycogen breakdown in prolonged endurance exercise.
Level 2 - randomized trial
Randomized crossover trial in humans
PubMed 32407242 · doi:10.1152/japplphysiol.00092.2020
What was done
In a randomized crossover design, 12 highly trained male cyclists completed a simulated race protocol consisting of 3 hours of intermittent cycling, a 15-minute time trial, and a maximal sprint. During the race, participants consumed 60 g carbohydrate/h alongside three boluses (25, 20, and 20 g) of either a ketone ester ((R)-3-hydroxybutyl (R)-3-hydroxybutyrate) or a control drink given 60 min and 20 min before, and 30 min into exercise. Researchers measured blood d-beta-hydroxybutyrate, pH, bicarbonate, net muscle glycogen breakdown, time trial power output, and sprint time-to-exhaustion.
What was found
Ketone ester intake increased blood d-beta-hydroxybutyrate to ~3 mM (range 2.6–5.2 mM; P < 0.001 vs. control), while blood pH decreased from ~7.42 to 7.36 and bicarbonate dropped from 26.0 to 21.6 mM (both P < 0.001 vs. control). Net muscle glycogen breakdown was similar between conditions during the 3-hour ride (ketone: -78 ± 30 vs. control: -60 ± 22 mmol/kg wet wt; P = 0.08) and the 15-minute time trial (ketone: -9 ± 18 vs. control: -18 ± 18 mmol/kg wet wt; P = 0.35). Mean power output during the 15-minute time trial (ketone: 273 ± 38 vs. control: 272 ± 37 W; P = 0.83) and sprint time-to-exhaustion (ketone: 59 ± 16 vs. control: 58 ± 17 s; P = 0.66) did not differ significantly.
Why it matters
Exogenous ketone ester supplementation does not spare muscle glycogen or enhance end-race endurance performance when adequate carbohydrate is provided, and it may impair systemic buffering capacity.
Limits
The sample was small (n = 12) and restricted exclusively to highly trained male cyclists, preventing generalization to females or recreationally active individuals. Blinding success and gastrointestinal symptoms were not detailed in the abstract.
Cited by
- contradicts Beta-hydroxybutyrate has been shown to enhance physical endurance.