New Urbanists' claims that sprawl causes obesity were suspect the moment they were first uttered. Recent research by Siim Soot and his colleagues at the University of Illinois, suggests that even the correlations do not stand up.
U.S. DOT's periodic NPTS/NHTS passenger travel surveys can be disaggregated by "central city" vs. "suburban" place of residence of each respondent and there have never been significant travel pattern differences between these aggregates.
It is a simple point but it bears repeating because the NU crowd is eager to rearrange other people's lives (for those people's own good, of course).
In the March 2006, Journal of Economic Literature, there is a fine review (by Angus Deaton) of Robert Fogel's The Escape from Hunger and Premature Death, 1700-2100. Deaton writes, "... explosions of obesity and associated diseases ... often come on the heels of a looseing of nutritional constraints, when those whose parents were undernourished, who were themselves undernourished in utero, move into an environment in which food is plentiful and heavy manual labor is no longer required."