I think its all about peoples perception of "you"....those who know you, are used to you, and are comfortable with you as you were. The human race does not adapt well to change, and seeing you changing will be bringing up all sorts of questions, thoughts, ad emotions within the people who are making comments. Don't forget how bullies operate, they make someone else feel bad to make themselves feel better. Your change makes them feel uncomfortable, and threatened because on the whole, people talk a lot, but never make things happen, and seeing one of the few who put thoughts into action makes people very uneasy.
If you met someone new tomorrow, they wouldn't comment on your weight, because that would be how they know you. Nobody ever meets a new friend and says "oh you're too skinny", it's all perspective......to those who have been in the 9 stones their whole lives, the thought of being 12 stone for example would fill them with dread. To those who have been overweight their whole lives, 12 stone seems like an amazing achievement - and it is!
People have defence mechanisms, we like to protect ourselves, and our bubble. They feel threatened by your success, and they're lashing out. The comments are not true, nor are they justified. Just hold your head up high, keep going until you get to goal, and then stay there, they'll soon get used to the new you and the comments will stop. If they don't replace them with new friends
Live life for you and let the haters hate xxx