Effects of Low-Carbohydrate and Ketogenic Diets on Aerobic Performance in Trained Athletes: A Systematic Review and Meta-Analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized trials
PubMed 41829910 · doi:10.3390/nu18050740
What was done
A systematic review and meta-analysis of 33 studies identified across five databases (PubMed, SCOPUS, Web of Science, SPORTDiscus, and Cochrane Central Register of Controlled Trials) evaluated the effects of low-carbohydrate (≤130 g·day⁻¹ or ≤25% total energy) and ketogenic (<50 g·day⁻¹ or <10% total energy) diets versus high-carbohydrate control conditions. Participants were trained athletes aged 18–45 years with at least 6 months of structured training. Outcomes included VO2max, time trial performance, time to exhaustion, exercise economy, fat oxidation, and substrate utilization. Study quality was assessed with the Newcastle-Ottawa Scale.
What was found
Fat oxidation increased in all 30 studies measuring it (+28% to +200%). VO2max was preserved in 50.0% of studies and improved in 11.1%. Time to exhaustion performance was maintained in 69.2% of studies. Submaximal exercise economy was impaired in 50.0% of studies. Temporal analysis demonstrated that testing within 7 days or fewer showed performance decrements, while testing at more than 1 week consistently showed maintained or improved performance.
Why it matters
This review identifies a clear one-week adaptation threshold for endurance athletes transitioning to low-carbohydrate diets, showing that acute performance decrements rebound once fat oxidation increases, though exercise economy may remain compromised.
Limits
The abstract reports counts and percentages of studies rather than pooled numerical effect sizes or confidence intervals. Total participant count across the 33 studies is not stated. Submaximal efficiency was impaired in half of the studies, presenting an unresolved limitation for high-intensity efforts.
Cited by
- partial Athletes following a ketogenic diet did not experience deterioration in physical performance compared to those on a high-carbohydrate diet.