That doesn't seem right? https://www.cdc.gov/mmwr/volumes/66/wr/mm6650a1.htm sounds like the general trend is obesity declines with income and education, although more strongly for some demographics and negligibly for others
Obesity declining with income doesn't mean less calorically intense food is cheaper, it just means that higher income better educated people eat less calories.
That still creates a correlation between income and obesity.