A Question About Anorexia...?

I have a friend and although her anorexia began quite gradually, by the time she started starving herself (as in not consuming any solids, only drinking water and exercising constantly) after two months, she seemed to have dropped about two/three stone. Is this possible? I mean, once the human body starts starving, is it really possible to lose that much weight in such a short space of time? Because I'm not sure if she lied to me and was actually starving herself for a lot longer, as I can't understand how someone could lose so much weight so quickly. Thanks.