In this comprehensive review, Noakes, Volek, D’Agostino and colleagues synthesize a large body of controlled trials and metabolic studies showing that low-carbohydrate, high-fat (ketogenic) diets fundamentally alter how athletes fuel exercise. Contrary to the long-standing “crossover” concept—which holds that carbohydrate must dominate energy production at moderate to high intensities—the authors document that keto-adapted athletes can sustain very high rates of fat oxidation at intensities well above 80–85% VO₂max, without impairing performance. These findings challenge the assumption that carbohydrates are an obligatory fuel for high-intensity exercise.

Beyond performance, the review highlights an underappreciated health dimension: a substantial proportion of endurance athletes consuming high-carbohydrate diets exhibit pre-diabetic glucose patterns, despite being lean and highly trained. Across multiple studies using continuous glucose monitoring, these dysglycemic profiles resolved when athletes switched to a low-carbohydrate or ketogenic diet. The authors argue that dietary carbohydrate load, insulin signaling, and mitochondrial function are tightly linked, and that ketogenic diets may both expand metabolic flexibility during exercise and improve long-term glucose homeostasis—even in athletic populations.

https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2023.1150265/full