The causation you're indicating is not clear at all to me. You seem to be saying, "Poor people prefer Big Macs therefore that's what they get, and no grocery stores."
But an equally valid observation is that the lack of grocery stores and the presence of fast food and gas stations/corner stores produce an apparent preference without indicating a real preference.
Food deserts doesn't exist in most countries though, it is an American thing. Nowhere else is it hard to go find basic groceries you can use to cook anywhere.
I don't get your point with this comment. bedhead suggested that Big Mac consumption by poor people leads directly to their food desert problem, my comment is that that causal order is not clear. An apparent preference can be created by lack of choice, not by actual choice.
Do people in food deserts prefer Slim Jims from the corner store and Big Macs or does it seem that way because of a lack of choice?
But an equally valid observation is that the lack of grocery stores and the presence of fast food and gas stations/corner stores produce an apparent preference without indicating a real preference.