Because of the massive amount of sugar that Americans eat on average, most people have become dependent on glucose, instead of fatty acids, for energy. Every supermarket, grocery store and coffee shop sells an abundance of sugary foods and drinks. When you eat a lot of sugar, and that sugar isn't utilized for energy, your body breaks it down and eventually stores it as body fat.
Not only that, but growth hormone is increased during fasted states (both during sleep and after a period of fasting). Combine this increased growth hormone secretion:, the decrease in insulin production (and thus increase in insulin sensitivity ), and you’re essentially priming your body for muscle growth and fat loss with intermittent fasting.