In a double‑blind, placebo‑controlled trial with eighteen trained cyclists, 25 g of a ketone monoester taken after each stage and before sleep failed to improve recovery, cognitive markers, sleep quality, or endurance performance during an 8‑day simulated stage race.
Study and findings
Eighteen well‑trained cyclists were allocated to either a ketone monoester (KE) group (n=8) or a taste‑matched placebo (CON) group (n=10) in a parallel, double‑blind design. Over eight consecutive days, participants completed a simulated stage race while receiving 25 g of KE immediately after each stage and 30 minutes before bedtime. Primary outcomes included heart‑rate response, a 30‑minute time‑trial performance, mechanical efficiency at 200 W, substrate oxidation, sleep metrics, and muscle biopsy markers. The race induced expected fatigue: peak heart rate fell by roughly 11 bpm and time‑trial power declined by about 3 % across both groups. In the KE group, mechanical efficiency at 200 W decreased and fat oxidation increased by 120 % relative to baseline, an interaction that reached statistical significance (p=0.028). No differences were observed between KE and CON for sleep duration or quality, dietary intake, or skeletal‑muscle biochemical markers (p>0.05).
Clinical interpretation
The data suggest that, under the conditions tested, acute ketone monoester supplementation does not confer measurable advantages for recovery of aerobic performance, cognitive function, or sleep during prolonged multi‑day endurance effort. The observed reduction in mechanical efficiency and the marked rise in fat oxidation in the KE arm may reflect a metabolic shift toward ketone utilization that does not translate into performance preservation. Because both groups experienced comparable declines in heart‑rate and time‑trial output, KE cannot be considered an effective strategy to attenuate the physiological strain of consecutive endurance stages.
Limitations and open questions
The sample size was modest, limiting statistical power to detect small effects, especially for sleep and cognitive outcomes that were not directly quantified beyond self‑report. The study relied on a single dose (25 g) and timing regimen; alternative dosing strategies might yield different metabolic responses. Moreover, the abstract does not detail the specific cognitive tests employed, preventing assessment of subtle neurocognitive changes. Future investigations should incorporate larger cohorts, objective neurocognitive assessments, and explore dose‑response relationships to clarify whether ketone esters can meaningfully influence recovery or performance in multi‑day endurance contexts.
Source
Engelbrecht L, Lauriks W, Robberechts R, Stalmans M, Ramaekers M, Terblanche E, et al. Ketone Ester Intake Did Not Improve Performance, Neither Cognitive Function or Sleep, During an 8-Day Simulated Cycling Race. Med Sci Sports Exerc. 2026. doi: 10.1249/mss.0000000000004119. PMID: 42658808.