Do you think losing 100lbs is like losing 200lbs?
There are people who get into this type of condition (severe obesity) even though they eat properly. But that's very rare, a lot of people just don't give a about what they eat and down a pizza every other day, etc. My aunt did it to herself and then had her stomach stapled. She ate too much and burst the staples, and ended up gaining more weight from over eating. She finally opted for the G.B. surgery and has lost a lot of weight due to reduced portions, but now she's gaining it back because of the type of food she eats.
Where as, my friend here in Houston who is very overweight has modified his diet to match mine exactly (mine is altered due to my in-ability to process fats cause of my galbladder removal) and he has lost 46lbs since January, with only a change to the TYPE of food he eats and how he cooks it. He doesn't exercise or eat less food. When he gets down to his goal weight, he will have lost over 150lbs and he should have it done in about a year or two, without having surgery.