Be honest here: have you ever read any research on this topic? It can be rhetorical but it is something to consider. I am willing to wager most people commenting here have not. There is a vast amount of research and data on this.
I hesitate to suggest a single article to read, but if nothing else, people should consider reading this:
Drewnowski, A., & Specter, S. E. (2004). Poverty and obesity: the role of energy density and energy costs. The American journal of clinical nutrition, 79(1), 6-16.
I'd be happy to provide the full text to anyone that can't access it. It is an older article that has been reaffirmed by major papers dozens of times and has been cited nearly 3000 times in other scholarly work.