I had a friend that did the same thing. She decided one day to just excersize her butt off, and 1 year later had dropped over 100 pounds (and is still small today). After doing that, she was very judgemental of everyone else that she knew that had a weight problem. As a matter of fact, we don't even talk anymore cause I just couldn't handle her "holier than thou" attitude. She started to get to where she would refer to everyone overweight as lazy and self-hating individuals. It got old really quick.

Maybe that's your co-workers problem and maybe it isn't. I've never understood how someone, even if they have found a way to loose weight, could be judgemental of people that are overweight. Shouldn't you be the example "skinny" person after you loose weight and understand that it is wrong to pass judgement on anyone because of the way that they look?