I've always been quite skeptical of the fast-food for the simple reason that when I am strapped for cash I buy rice and beans. No processed or fast foods even come close to rice and beans on a dollar-per-calorie basis.

So called "food deserts" are a bit of a chicken and egg problem. Are the restaurants in your area a reflection of the eating habits of the people in that area, or a grand conspiracy to keep us unhealthy? I tend towards the former.

I am also skeptical that even in "food deserts" an enterprising individual can't acquire rice and beans.

For people struggling to pay rent, sometimes working multiple jobs and or with kids, there isn't a lot of energy or executive function left. And even rice and beans aren't terribly nutritious. If that's a staple for decades it can also cause obesity, especially for certain genetic demographics.

Not to mention that when you are struggling to pay rent, you are often struggling to pay utilities too. Time without water, electricity, or gas to wash, cook, and keep things cold seriously impact your ability to cook, even if you do have the time.