Can you run just as well on a low-carb diet?

In athletes with normal blood sugar, it takes at least four weeks on a very-low-carbohydrate diet for glucose levels and ketone levels to stabilize, and for exercise performance to become consistent.

In trained male triathletes, following a very-low-carbohydrate diet for six weeks does not reduce endurance performance during prolonged exercise at 70% of maximum oxygen uptake compared to a high-carbohydrate diet, and the body maintains high-intensity endurance capacity even with lower muscle glycogen levels.

Trained triathletes who consume 10 grams of carbohydrate per hour during prolonged endurance exercise perform 22% longer before exhaustion, regardless of their usual diet, because this intake prevents low blood sugar during exercise without changing how the body uses fuel.

During prolonged endurance exercise, trained athletes experience low blood glucose levels below 3.9 mmol/L even without consuming carbohydrates; consuming a small amount of carbohydrates prevents this drop and enhances performance, showing that low blood glucose directly limits performance regardless of muscle glycogen stores.

Consuming 10 grams of carbohydrates per hour during endurance exercise increases the use of carbohydrates for energy and decreases the use of fat for energy by the same amount as following a high-carbohydrate diet for six weeks.