Fasting is the practice of abstaining from food for spiritual, health, or other reasons. It is an ancient tradition that is part of all major religions. We engage in fasting every day when we sleep. For those 6-8 hours when we are asleep, our body is repairing itself and using stored energy to do it. The longer you stay in this fasted state, the more stored energy your body uses. This is the basic concept of intermittent fasting.