Athletes who follow a more traditional diet use carbs as their primary energy source, but when your body is in ketosis the emphasis shifts to fats. The longer you have been on a keto diet the better you will be at using fat for energy. Don’t be surprised if your performance dips at first when you change to a keto diet, as you have to give your body time to adapt.
https://www.nutriminimart.com/f1-keto-oprah/
https://medium.com/@leslieeefoster/f1-keto-oprah-winfrey-dac530a5df68