I have never been the victim of body shaming and I don't know anybody who has.  But in my opinion, body shaming, or any kind of "shaming", is not a good thing.  People should never be made to feel ashamed of themselves because of their physical appearance.  First of all, you don't get to decide that a person has to look a certain way, in order for you to approve of their appearance.  However, if you want to encourage someone to pursue health, fitness, and well being, I'm sure you can do that without insulting the person.