I mean, even if we attribute 100% of the urban-rural difference to yuppy diet fads -- neglecting the almost-certainly much more important class, income, genetic

I mean, even if we attribute 100% of the urban-rural difference to yuppy diet fads -- neglecting the almost-certainly much more important class, income, genetic, and cultural differences -- the effect of those fads are being absolutely crushed by the general nationwide trends. Whatever it is that us urban people get out of talking about diet fad that people in the rural areas don't keep up with, I don't think it's motivated by a desire to understand the obesity epidemic.