I think Janicka is right that a lot of people use fasting for the purpose of detoxing. However, I have used Water Fasting to lose weight in the past, and after stopping my fast I kept the weight off. I found that once I started eating again (selective foods of course) The energy my body took from these foods was higher than ever before. So I used it to work out more while still controlling my eating.
I am in this process right now. I just completed a 6 day fast and I lost 8 pounds which I plan to keep off! I will keep you updated!