It's an epidemic of deliciousness. Seriously, though, about half of us are overweight. You can't blame people for being in the bottom 50%. There will always be people that put themselves in the fattest 3%, but we've got problems way bigger than a few people that can't control themselves. Everybody is getting fatter, not just fat people. That's what they are talking about when they refer to the obesity epidemic.
I know an obese "body positivity" person who is supposedly very positive about her self image (Why you would be positive about being overweight, I do not know) but makes a bunch of tumblr posts about horrid dietary choices and complaining about how fat and unattractive she is and how hard it is to work out as an unemployed women's studies major (?????) which garners a lot of cries of "you're beautiful!!!" from the hugbox that is the blagosphere. It's seriously hard to not tell her to just get some fucking willpower but I would end up having to burn a lot of bridges.