By contrast, he noted in an interview, people in cities are often forced to be active in their daily lives -- walking to stores and public transportation, carrying groceries up the stairs to their fifth-floor walk-up apartment.

And while suburban dwellers may be able to go to the gym for some exercise, research suggests many lack the time. This is again, in part, due to spending so much time in cars, commuting to work or driving to far-away stores and schools.

What's more, Ewing said, those cars have become "de facto snack shops" for many adults and kids, with the food often being fast food. In many spread-out suburbs in the U.S., fast food is the predominant dining option, Ewing noted.

All of this, however, is still speculation, the researcher said. The current findings, published in the American Journal of Preventive Medicine, can only point to a correlation between suburban sprawl and teenagers' weight.

But since Ewing's 2003 study, others have found a similar pattern. Even when accounting for other factors that influence weight -- such as race, family income and education -- the degree of sprawl seems to matter.

For the current study, which was funded by the U.S. National Cancer Institute, Ewing's team used data from a government survey that began following 8,984 12- to 17-year-olds in 1997.

They also used a county-by-county "sprawl index" that considers population density and street accessibility. The most compact, "walkable" county was New York County, which encompasses Manhattan; the most spread-out area was Jackson County, near Topeka, Kansas.

In general, the study found, more sprawl meant a greater risk of kids being overweight.

In communities where it's not possible for children to walk to school, or where they don't even have sidewalks to use, parents may need to make an effort to help their kids get active, according to Ewing.

"Get them away from the TV and get them into sports or some organized activity," he suggested.

A more drastic alternative is to move.

Ewing said a growing number of U.S. communities are recognizing the pitfalls of sprawl and devising "new urbanist" designs -- creating old-fashioned, pedestrian-friendly Main Streets, better public transportation and "mixed-use" zoning that places residential and commercial buildings near each other.

SOURCE: American Journal of Preventive Medicine, December 2006.

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