Sprawl has been accused of many evils, but here’s a new one: It may make you fat. While suburban residents drive to get most places they go, many city dwellers walk or ride bikes, and that physical exercise seems to keep urbanites slimmer. “[I]f you choose to live in a sprawling environment, you are more likely to be overweight,” says Lawrence D. Frank, a professor of urban planning at the University of British Columbia and author of a new study on the links between sprawl and obesity. His research seems to make a case for more dense, mixed-use, pedestrian-friendly development. In the U.S., the cities best suited for walking are Boston, Chicago, New York, San Francisco, and Seattle, say urban planners. Least walker-friendly are Atlanta, Houston, and Phoenix — low-density metropolitan areas with high rates of obesity and diabetes.