Research

Macro partitioning

Seven days of a short-term ketogenic diet (KD) in endurance-trained males significantly increases maximal fat oxidation rates (approx. 1.8-fold) and shifts substrate utilization toward fat, while simultaneously causing a loss of both fat mass and fat-free mass.

If you are an endurance athlete, switching to a strict ketogenic diet for just one week will significantly boost your body's ability to burn fat during exercise. However, expect to lose about 2.4 kg of body weight, which includes both fat and some fat-free mass (likely partly water/glycogen). Your maximal power output and aerobic capacity remain unchanged in the short term, but be aware that high-intensity performance may suffer in longer-term adaptations not captured here.

ModerateSupportsMEDIUM confidence
Short-term KD results in loss of both fat mass and FFM, increased rates of fat oxidation and a concomitant reduction in CHO utilization even at moderate-to-high intensities of exercise.
Fionn T. McSwiney et al. · Biology of Sport · 2020

Why this rating

Small sample size (n=9), single-arm pre-post design without a control group, and short duration limit generalizability.

Source

Changes in body composition and substrate utilization after a short-term ketogenic diet in endurance-trained males

Fionn T. McSwiney et al. · Biology of Sport · 2020

DOI 10.5114/biolsport.2020.98448

crossover · n=9Cited 18×
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DOI resolved against Crossref · corpus check 2026-06-10

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