My guess is that higher obesity rates in both the nation as a whole and the South in particular are the result of a combination of a decline in manual labor due to automation on the job and at home, the effects of food additives, notably high fructose corn syrup, and a tendency of lower income people, irrespective of race or ethnicity, to purchase prepackaged and prepared foods with high starch and fat contents.
Agreed. The effect of weakened families cannot be discounted. I would bet that a large number of these low income people are from single income families or families where both parents work. Traditional Southern cuisine may be fattening, but so are other regional cuisines or ethnic fare. Income and race/ethnicity are factors, but so is family structure. Mormon dominated Utah has the second lowest level of obesity; Mormon divorce rates are below average. (Additionally, LDS theology has emphasized healthy lifestyles.) The states north and east of Pennsylvania, which are heavily Catholic, have below average obesity rates, in spite of the popularity of carbohydrate dense Italian cuisine and Irish food (meat and potatoes, sort of like Southern, but without the African and French/Latin influences). Northeastern divorce rates are below national averages. The Upper Midwest generally runs to the national average despite the large German-American population and the traditionally heavy nature of German cuisine (and beer). These states, which are heavily Lutheran and secondarily Catholic, have below average rates of divorce, though not quite as low as the Mormon and Catholic dominated states.
The high obesity rates in West Virginia, Oklahoma, and Kentucky, all three Border states, are not attributable to large minority population, but rather the low income and high divorce rates. Evangelicals and fundamentalists, black or white, have not done a good job in maintaining families when compared to other religious groups or even atheists or agnostics. Of course, divorce and sexual and familial irresponsibility have increased across the board for 90 years. But evangelicals and fundamentalists (which I am) have helped to lead, rather than trailed, the pack.