I think it's different insofar as somehow obesity becomes a morality issue, that and the fact that women's bodies and what we do with them is always up for commentary. A person with anorexia doesn't really receive the kind of snide remarks as fat people often do. It's an actual disease, so it's really not about forcing anyone to do anything. So I really think society is far more concerned with obesity than w/anorexia.
There is far more at work here than just an issue of health... there is a fierce element of personal politics too.
Thin is a beauty standard, prized, revered, rewarded, strived for. No question. The gray area that starts to become 'too thin' is often ignored in favor of the positive connotations that go with thinness (look at the fashion industry! the movies!), unless it gets really, really bad. This makes it NO LESS of a dangerous health issue, absolutely. BUT the thin RARELY have to fight the overwhelming crush of stigma, even in their health issues, that fat people face. Thinness is not seen as a character flaw, even in its most extreme state.
Fat is (hear me out, this isnt MY personal words, but can be agreed upon as a long held societal standard) not attractive, lazy, stared at, looked down on, almost a character flaw. People try to hide it, fight it, all matter of combat because frankly, they need to. Society does not favor the fat. So fat people have it extra hard. Not only do they probably want to lose some weight, they also have the weather a constant shame that goes with being fat.
The hesitation, in my opinion, sometimes to address health issues when it comes to fat people is that, in some sense... fat people KNOW they are fat, they get it every single day. They cannot be totally ignorant to the consequences. To some extent it is natural to react in a way like 'hey, maybe we should back off of these people for once,' I am not saying this is the way to help people become healthier, but I can almost understand the attitude.
As for me personally, I will ALWAYS stand by the idea that, no matter WHAT, the only person that has to live with your body is you. You are the only person your body should concern, good, bad, everything. You have no responsibility to your family, your friends, society, in regards to your body in any way shape or form. It should never concern anyone else and you shouldn't have to answer for it.
The only way people as a whole will get healthy in decades to come is also the only way anything is going to get done in this country: by embracing personal responsibility. So I say, lets just leave people to find their personal responsibility and worry about our own.