Volek et al. 2016, FASTER: metabolic characteristics of keto-adapted ultra-endurance runners

Metabolism 65(3):100-110, DOI 10.1016/j.metabol.2015.10.028. Cross-sectional comparison of 20 elite ultra-runners and triathletes habituated to either a high-carbohydrate or a low-carbohydrate diet (mean ~20 months). Peak fat-oxidation rate was 2.3-fold higher in the low-carbohydrate group, the highest yet recorded; resting and post-exercise muscle glycogen were similar between groups. Establishes how high fat-oxidation can climb with long-term keto adaptation. Observational, not a performance trial.