Even though elite race walkers get better at using oxygen overall on a keto diet, the diet makes their bodies use more oxygen during race pace, so their performance doesn’t actually improve after 3 weeks.

Elite race walkers who eat lots of carbs or time their carb intake during intense training get about 5-6% faster in a 10 km race, but those on a keto diet don’t get any faster.

Elite race walkers who eat a super low-carb, high-fat diet for 3 weeks start burning fat like crazy when they exercise — one of the highest fat-burning rates ever seen in top athletes.

Elite race walkers who follow a keto diet for 3 weeks start burning fat for fuel during intense exercise, and their bodies show signs of ketosis — like having 1 mmol/L of ketones in the blood — even when working hard.

Even if elite race walkers don't change their diet, their stamina can still improve after a few weeks of intense training, as long as they're eating enough calories.

When endurance athletes eat a high-fat diet for 6 days, their bodies burn less carbs during a long bike ride compared to when they eat a high-carb diet — showing their metabolism switches to using more fat for fuel.