I think people make comments like that because when you try to make changes, it underlines something in their own lives which says "I need to change/eat better/exercise more" and they don't like to be reminded that they need to change or of their failure to change. They have a go at you when really they are trying to pass the invisible buck and escape the realisation about just how bad they have let themselves get!
Rest assured that every time they pass comment, its because you have outlined to them their failures and they do not like it. Its not about you, its about them.