Only Colorado and Washington, D.C., had obesity rates under 20 percent. Researchers are not sure why. Dr. William Dietz, director of the nutrition, physical activity and obesity division, said that Colorado had spent money from a state lottery on biking and walking trails and that many people were using them. The state seems to have “a culture of physical activity,” he said.
Dr. Dietz said the relatively low prevalence of obesity in Washington was harder to explain, particularly because the area has a large black population.
He said one explanation may be that many residents ride the subway; studies have shown that compared with people who drive, those who use public transportation tend to be thinner because it involves more walking. In addition, Dr. Dietz said, there is evidence of above-average fruit and vegetable consumption, and higher rates of breast-feeding, both of which are linked to lower rates of obesity.
http://www.nytimes.com/2010/08/04/health/nutrition/04fat.html?hpw