Re: The problem
Hi, A.C.: While the people you describe certainly do exist, there is often more going on.
A lot of people are "nutritionally clueless", but since many folks (for better or worse) get their "education" from teevee, I'm not sure how they'd know better. So agree that we need more and better education on nutritional bang for the buck. To this end, at least around here, some schools are incorporating "community gardens" into class curricula so the sprogs can learn nutrition, math(s), nature/science, and so on, and the kids generally love to eat the veggies that they grew themselves. Food for both brain and belly. I think the kids also take home any "surplus", but that likely varies by school.
Another problem is that poor neighborhoods often have few options for useful or real food. C-stores and "dollar stores" with overly processed packaged "food" dominate poor neighborhoods since the brightly-wrapped stodge tends to be cheap(-ish) and with enough preservatives to be shelf-stable. Real food, by contrast, tends to cost more and be perishable.
I'm not an expert, but my guess is that a lot of poor people are fat because the food to which they do have access is so nutritionally bereft that they need more calories' worth to get a decent supply of vitamins and other nutes. Just a guess on my part, there are likely other reasons.