Poverty is fattening. It's true. Starchy foods are cheap. Potatoes, Ramen noodles, rice, pastas, beans, breads. The cheap meats are loaded with fat. Cheap hot dogs, cheap bologna, almost-hamburger. Then there's the Dollar Menu at Gertie's Gallons of GreaseBurgers. It takes its toll.
Yes, it is possible to exist on these things and not become fat, but it takes intelligence, education, discipline, and the right frame of mind. It can be especially burdensome for those predisposed to weight gain, which has a lot more to do with being fat than society cares to acknowledge.
The idea that the economically challenged among use should be the skinniest is just not based in facts.