Why do some athletes follow a keto diet?

Ewoldt explains it like this: "Following a balanced diet that includes carbohydrates, a trained athlete can store about 2,500 calories of glucose, the preferred source of energy. But this same athlete has around 40,000 calories of fat available."

The idea is that by switching to a high-fat diet the body will adapt from using carbohydrates for energy to using fat. Because a vastly greater amount of fat is available, that would, in theory, keep endurance athletes like marathon runners or triathletes going longer. However, athletes do need some carbohydrate to use along with fat for energy. Ewoldt adds that the process of adapting your body from glucose-burning to fat-burning can take several weeks to months.