Yes and no. The other answer does a good job of getting into generalizations, so I’ll add onto that because otherwise it’ll get too technical. Junk food often gets a lot of the blame for making Americans fat.
Part of the issue, however, is that we’re not giving people who cannot afford to buy all fresh fruits and vegetables a choice in what they eat. They most likely have to buy the junk food because it’s all they can afford. In addition, Americans don’t exercise as much as we once did. Many people rely on cars to get to work, to school, and other places.
Kids don’t play outside because the parents are afraid they’ll be harmed or the cops will be called even if they’re watching from the window.
So, while some junk foods will certainly attribute to being fat (mainly the sugar craze), it’s not the only factor.