If you want to learn more you can read this
http://drsquat.com/articles/zigzag.html oh and you dont have to work out 2-3 hours a day. 30-45 min 6 times a week, or 1 hours 3 times a week is MORE than enough. The diet will take care of the fat.
although not 80lbs, I did work with my girlfriend and had her loose about 65lbs In a couple of years. It took that long, because it was hard for her to make changes in the beginning (and she was a major flake). Problem with that was she like exercising and now is trying to bodybuild and get "big".
I myself gained 90lbs using those methods (halfassed cause I am a flake too) it took about 7 years.
If you go with your doctors, their diets will work, but usually cause lots of insulin spikes, because of what they recommend, and the persons end up looking very soft. Doctors are trained to work on sick people and not healthy people, and are usually fat themselves.
either way whatever you decide to do GOOD LUCK!