(Here's a figure showing how it actually costs more to feed a family of 4 unhealthy stuff from McDonald's than it does to feed that same family a healthier meal from foods bought at the grocery story.)
Moving on, here's the biggest roadblock: it takes too much time and effort to cook. This used to be my roadblock. But as Mr. Bittman explains, it's really not that time-consuming to cook compared with how much time people spend watching TV. Yet it's all about perception, not facts. And the most important perception in all of this is that cooking is work and not something pleasurable.
Quoting from the article: "People really are stressed out with all that they have to do, and they don’t want to cook," says Julie Guthman, associate professor of community studies at the University of California, Santa Cruz, and author of the forthcoming "Weighing In: Obesity, Food Justice and the Limits of Capitalism." "Their reaction is, 'Let me enjoy what I want to eat, and stop telling me what to do.' And it’s one of the few things that less well-off people have: they don’t have to cook."
Other reasons for people picking fast food (or packaged meals you heat up in the microwave) over eating healthier food are mentioned, such as added sugars and fats that are addictive, $4.2 billion dollars being spent on marketing this stuff, and the existence of "food deserts."
So there's a lot of reasons, biological and psychological, preventing people from adopting a healthier diet. I hope this essay dispels one of psychological barrier that is completely unfounded. Healthier food, it turns out, is actually more affordable than junk.