America's Obesity Crisis:Exercise: The Walking Cure

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A serious effort to examine that connection got under way at a meeting convened in 1997 by the Centers for Disease Control and Prevention (CDC). To get people in different disciplines to start thinking about an obesity-sprawl connection, the CDC brought together city planners, architects, researchers, transportation engineers and even criminal-justice experts. (Why criminal-justice experts? Because safer streets are more walkable. There are a lot of pieces to this puzzle.) That meeting was a catalyst for the rise of the active-living movement, which got a major boost two years later when the Robert Wood Johnson Foundation, a philanthropic organization with an interest in health-care issues, stepped in with grant money.

One of the most important studies in this new field was published last summer. Led by Reid Ewing, research professor at the National Center for Smart Growth at the University of Maryland, the study examined data on more than 200,000 Americans living in 448 well-populated counties (nearly two-thirds of the U.S. population lives in those counties). Ewing found that people in sprawling counties weighed more than those in more compact ones. Residents of the most spread-out locale, Ohio's Geauga County, outside Cleveland, weighed on average 6.3 lbs. more than those living in the most condensed, Manhattan. Geauga County residents were also 29% more likely to have high blood pressure than New Yorkers. (So much for the stresses of city life.) One possible reason: people who lived in the 25 most sprawling counties walked an average of 191 min. a month, compared with 254 min. a month for those living in the 25 densest counties. "And there are thousands of Geauga counties," says Ewing. "There are very few really walkable places."

Even more detailed evidence of the obesity-sprawl connection appears in a new study led by Lawrence Frank, a professor at the University of British Columbia in Vancouver. Frank surveyed nearly 11,000 people in Atlanta, compiling their body mass indexes (BMIs) and correlating those figures with the characteristics of the neighborhood within a kilometer of their homes, including whether shops and services were mixed in among the homes. He asked participants to keep a travel diary for two days to record where they went and how they got there.

What Frank discovered was that for every hour people spend in their cars, they are 6% more likely to be obese. For every kilometer--just over a half-mile--they walk in a day, they are 5% less likely to be obese. And if they live in a mixed-use environment (one in which there are shops and services near their homes), they are 7% less likely to be obese--probably because they walk more. "The policy implication of this study," says Frank, "is that if we're going to solve our public-health issues, we're going to have to address the built environment."