Depends on the person really. I remember reading on here how someone fasted for 10 days and lost 1 pound boy were they mad and I did not hear from them again. So, it is hard to say. But only trying and time will tell:-)
You will put on food and water weight when you come off a fast. About 10 pounds or so. But that link above you can plug in your numbers to see the loss that will stick.