Sacred Haven of Debauchery

McDonald's is a joke; only the pies are edible.

And the pies are the only inedible item at McDonald's. You sit there for half an hour, take a bite, and you still burn your tongue. And that overly sweet filling. Nobody buys them, and that's why they try to push them on you with every large order: "Would you like a pie?"
Americans are fat because the food in their country is garbage. If they eat a bowl of cereal with milk in the morning, the best they can do at home is eat frozen ready-made meals. These housewives in the suburbs who "cook" are essentially just defrosting ready-made meals that they bought at a 24/7 store.
But it's much easier to drive to KFC or Burger King, where they can get a tasty, albeit excessively fatty, meal for a reasonable price.
Secondly, they are not very active; they all drive everywhere – from family minivans to old, beat-up grandpa's pickup trucks. They really don't like to walk, and therefore they can't burn off their fat.
Thirdly, they often order the same fast food to their homes, sitting on the couch, peeling open another Bud or Miller, and watching "the game," which, again, affects their weight.

That's how it is. And it's not about stereotypes.