In fact I think America's poor have a bigger problem with obesity than starving.
Of course, part of the reason for that is food insecurity. If you don't know where your next meal is coming from, when somebody hands you $3, you buy the biggest bag of potato chips you can, and you eat it NOW, before somebody else finds out you have it.
Candy bars are way easier to shoplift than whole wheat bread and organic spinach.
If you're dumpster diving: sell by dates on produce are usually... optimistic. I've had dairy go bad before the timestamp too. But if you find pie or cookies past their sell-by date, they're probably fine.
Getting regular exercise is more difficult for poor people too. (Gym memberships? Biking in crappy neighborhoods where your bike gets stolen? Whenever-your-sadistic-boss-wants-you-to-work work schedule plus single-parent commitments...)