I'd read for years about autophagy (when your body breaks down old cells and replaces them with new cells). When you fast, your body doesn't have to break down food, and can repair & cleanse itself.
Over the course of 21 days I lost 20lbs, and managed to keep most of it off. I was hungry a lot of the time, but, surprisingly, it was bearable!
When fasting, you have to keep your electrolytes in check. Your body needs these essential minerals (magnesium, potassium and sodium) to thrive. When you don't take enough you begin to feel foggy.
I also drank plenty of water and herbal teas to stay hydrated and full. It definitely helped keep cravings at bay. Visit my full blog post for the daily fast breakdown.