It's not just about affordability, it's also about education. Plain rice, flour and the like are much cheaper per calorie/nutrient than junk food, and healthier

It's not just about affordability, it's also about education. Plain rice, flour and the like are much cheaper per calorie/nutrient than junk food, and healthier, but many people simply don't know how to cook. I know families in Asia, for instance, who while being almost an order of magnitude poorer than the American poverty line are still a lot healthier, because they know how to prepare their own food from staples.