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.