Why are Americans, on the aggregate, unhealthy and fat? Certainly it has a lot to do with bad calories being the cheapest calories to produce; but beyond that, Americans lack a food culture. Food cultures are cultural attitudes toward eating. A food culture says, “Eat this, not that, and at these times.” Violating a food culture is taboo; it goes against societal norms, so people avoid it.
Americans do not have food taboos. We do not know how to eat, and the food industry probably wants to retain this status quo. Our lack of a food culture means that eating is thrown into chaos.
For example, it has become not only acceptable, but expected that snacks be available to munch on throughout the day. That much additional food amounts, effectively, to a fourth meal: breakfast, lunch, dinner, and all the snacks in-between.
Many local communities still pay homage to ancestral food cultures (America is a melting pot of immigrants, after all), but as older generations fade away so too does their food philosophy.