Based on a standard 2000-calorie diet, a diet consisting primarily of calorie-dense foods costs $3.52 a day, but a diet consisting primarily of low-calorie food costs $36.32 a day.
I'll need a few minutes to read the study, I'll admit. But I don't think that a day's worth of dry beans and dry rice costs $36. You can buy foods that are high in both calories and nutrients. The problem with food from McDonald's isn't so much that it's high in calories, but that it's really low in nutrients (and also contains too much not-so-great stuff). You probably won't feel as good 2 hours after eating it as you would if you'd eaten an equal number of calories with a better balance of nutrients. Eating fast food may encourage you to eat more, which means spending more money on food.
However, it's true that poor neighborhoods often don't have a decent grocery store. I forgot about that. And it's also true that preparing any food takes more effort than pulling up to a drive-through, and you may not have the energy to do that after a long hard day. Plus, since the fast food means that someone else does the work for you, it can really feel like a luxury.
I've heard "healthy food is too expensive" from people who spend more money on ice cream, cookies, and chips than they do on actual "meal" foods like bread and meat. I also had that in mind. Yeah, I'm really bourgeois And no, I don't act judgmental toward those people, or mention it to them.