If I'm 140 lbs how much weight can you lose if you starve myself for 3 weeks?
Starving yourself is not the way to go. You could die. Your vital organs can be damaged and much muscle lost. It can backfire and cause you to be worse off in the long run as your body metabolism will then start to put everything on as fat rather than burn it. Please don't do this. There are much better, less damaging and permanent ways to make a difference. Please seek out a medical opinion as to the best option for you and maybe contact a weight loss center and check out the information now available on low GI eating which produces results where other diets fail. In that way it can be a whole new life for you rather than the opposite.