Poor nutrition and a sedentary lifestyle do cause health problems, in people of all sizes. This is why it’s so fucking crucial to separate the concept of “obesity” from “eating crap and not exercising.” The two are simply not synonymous — not even close — and it’s not only incredibly offensive but dangerous for thin people to keep pretending that they are. There are thin people who eat crap and don’t exercise — and are thus putting their health at risk — and there are fat people who treat their bodies very well but remain fat. Really truly.