It definitely is possible since a lot of it is water weight. It depends on how much excess water weight you are retaining. Keep in mind that one person can lose that much fasting while someone else fasting that long may only lose a few pounds. But the body is doing what is best for you. It might have more important things to do first like help an artery that is getting clogged. Also experience with thousands have shown that the fatter you are, the faster you lose weight on a fast.