A lot more people were "concerned" for me when I was a little bit chubby than they ever were when I was anorexic, starving myself, seeing stars every time I stood up, hair falling out, no period, about to be admitted to hospital for my eating disorder. For that, it was all "well done!" and "look how fit an athletic you are now!". My favourite from my grandmother "you look like a pretty little doll now!".
You cannot judge someones health by their appearance. I was a million times healthier chubby than I was at my lowest. I was treated a million times nicer at my lowest, too, with a lot more compliments and general tone of respect when people spoke to me.
Fuck all to do with health. All to do with appearance.
The treatment and remarks against fat people, for the most part, have fuck all to do with health in general.
That includes from mothers to daughters, from husbands to wives. The recipient of the comments KNOW when it's just concern, as it's an open discussion, and they KNOW when it's people just being shitty about them not being skinny, because it's just people being shitty. Trying to make out that fat people just confuse the two (to excuse your own bigotry and desire to bully) is absolutely deluded.