Tyler Cowen linked to a Time article on the phenomenon of Southern Americans being relatively overweight vis-a-vis Americans from other regions of the country. Several reasons are offered, from the lower per capita income of Southern states, to the fact that Southern food tends to be fried and less healthful. But the article doesn't mention one very salient fact: black Americans are heavier than white Americans, and are disproportionately concentrated in Southern states. What is a regional disparity could be accounted for by underlying differences in the distribution of races. State Health Facts reports that 70% of African Americans are overweight, vs. 60% of white Americans. Using state-by-state data one can see how accurate assessments of interregional variation are when you control for race. The chart below shows the relationship between the proportion of whites who are overweight to the total population in each state*.
As you can see, there's a relatively close relationship between white overweight rates and total overweight rates. This makes sense since ~2/3 of the latter is composed of the former. There are many states, such as New Hampshire, where the white (non-Hispanic) rate for any given statistic is an excellent approximation of the total rate. On the other hand, there are states such as Hawaii or Mississippi where the white rate for a statistic shouldn't necessarily be used as a proxy because of a large non-white population. I say not necessarily because there is likely to be some correlation between white and non-white values in a given state (this is evident in the South where the whites exhibit social views closest to black Americans when set against other regions of the nation). So, what is the correlation between black and white rates of being overweight by state? In other words, do black and white Americans vary in weight by state in a similar manner, or are they totally uncorrelated? Again, I looked for data at State Health Facts. Because of the sample size for blacks was very small in many states I eliminated those (the cut off was determined by State Health Facts, with those states being left empty). Additionally I removed Washington D.C. from the data because whites and blacks exhibit such a huge difference that this is an outlier. Only 38% of whites in the District of Columbia are overweight, while 66% of blacks are. This is probably due to the fact that D.C. isn't equivalent to a state, but is a segregated city. The issue of size of course distorts regional assessments on a state-by-state basis, as California or Texas probably have more variation within them than many groups of states (e.g., the Upper Midwest states for example), so the results below should be interpreted cautiously. In any case:
33% of the black overweight rate variation between states can be predicted by the white overweight rate variation. There is some general underlying commonality then even when you account for race by region which causes disparate rates of being overweight. Obviously blacks and whites in the South both share the experience of living in the same climatic regime, and also aspects of their culinary traditions. Finally, there are obviously other variables. How about looking at the % in a state who are "low income," defined as no more than 200% of the federal poverty line.
Only 17% of the variance in being overweight can be explained by the proportion who are low income when it comes to federal criteria. Since this doesn't take into account huge national differences of cost of living, I suspect that these data probably exaggerate the real variance of weight explained by income. I suspect that 17% is higher than it would be if these factors were taken into account. Finally, a table which shows the states where there are enough blacks to be counted for in the data, and the black-white difference in proportion who are overweight. Note that in Wisconsin the black and white overweight rates are almost matched.
* I mislabeled the as "obesity" what should have been "overweight," just just replace appropriately.