Ray Cronies, the author of hypothermics.com , did 24 day fast while properly measuring what body uses for fuel. It turned out that it was only fat with no any s

Ray Cronies, the author of hypothermics.com , did 24 day fast while properly measuring what body uses for fuel. It turned out that it was only fat with no any significant muscle loss. This matches from what I read experience of people doing even longer fasts for medical reasons. The moment when body runs out of fat reserves happens after about 40-60 days of fasting when one starts to feel very strong or even uncontrollable hunger.