[Poor folks have poor ways...]
I am not trying to denigrate anyone who is poor, but truthfully many of them are the ones eating fast food all the time and end up overweight. It’s strange.
Time is money. You can have a nutritious, balanced diet for very little, if you have someone with the time and skill to cook it. That's been the norm for most of human history. But if you're working two jobs to make rent, you don't have a couple of hours when you get home to get dinner ready.
Not to mention that poor neighborhoods usually don't have a big Kroger or Publix or Safeway. They have a crappy little grocery that makes more money from cheap beer and lottery tickets than from food, where the "produce" section is a few squishy tomatoes and a couple of wilted heads of iceberg lettuce.
Paradoxically, it's awfully expensive to be poor. That's why obesity has replaced malnutrition as the main nutritional problem among poor Americans. It's a relatively new problem that needs new and clever solutions -- like neighborhood food banks, and maybe some sort of volunteer or cooperative arrangement -- say, one person volunteers a few hours one day a week to cook a nutritious dinner for a dozen families. Line up one such person for each day of the week, and that's a big step.