A person with a crippling addiction to sugar is going to look like a morbidly obese person. A person with a crippling addiction to heroin is going to look like that homeless person you're picturing. But the obese person can have sugar delivered to their door on a daily basis, and the drug addict has to do some sketch shit to maintain their addiction.

Most people are far further down the scale than either of those two obvious examples, and may be indistinguishable from someone who isn't actively addicted to something. Though, the 40% obesity rate night have something to do with that.