Thin population: urban sprawl and obesity.

IT WAS BAD enough when urban sprawl was charged with destroying community and turning us into selfish bastards. Lately it's been blamed for bloating our waistlines, turning us into fat selfish bastards. Sprawl critics claim geographical spread leads to bodily spread by encouraging people to drive rather than walk or bike.

But a recent study by researchers at the University of Illinois at Chicago casts doubt on that theory. A team led by Siim Soot, director emeritus of the university's Urban Transportation Center, used the heights and weights reported on driver's licenses and state ID cards to calculate the body mass indexes (BMIs) of 7 million northeastern Illinois residents, then analyzed the relationship between BMIs and the demographic characteristics of 300 ZIP codes. "There is scant evidence that obesity is directly associated with urban sprawl," they concluded. In fact, Chicago's inner suburbs had the lowest BMIs.

Soot and his colleagues did confirm conventional wisdom about obesity in some respects, finding that "individuals living in high-income areas with high levels of college educated residents and high home values are more likely to have low BMIs than residents of other neighborhoods," while residents of poor neighborhoods are more likely to be fat. But they argued that earlier research using county-level data may have generated a misleading association between sprawl and obesity by concentrating on the largest counties and averaging together high-and low-density areas within each count). They also noted that such research does not show, a statistically significant relationship between sprawl and lower levels of exercise, the factor that supposedly makes suburbanites fatter than city dwellers.