Sometimes when we are in the process of critically thinking about ourselves, trying to see where we are weak and what we need to change we go into hyper critical stage of both ourselves and others. The important thing is that you are aware that this is not something you aren't happy about and that you are careful not to respond to those thoughts and feelings. I think it helps us all, whether we are judgmental of someone's weight or hair or whatever to try to look at them as human beings and be empathetic. I am not saying pity them but imagine how they would feel if they knew you were thinking that about them. Then it would personalize them and connect you with them on some small level and allow you to have a change of heart about them as a person as opposed to some "heavy person". I know you aren't a bad person and you want to change and that gives you a big advantage over others who don't know better. Good luck.