Colorado is the least obese state, according to the “increasing girth rate” graphic in Tuesday’s Washington Post. Just 19.1 percent of its population had a body mass index of 30 or more in 2009, making it the only state in the union with an obesity rate of less than 20 percent. Why are Coloradans skinnier than everyone else?

It could be their outdoor culture. A mountainous and temperate state, Colorado is well-known for hiking, skiing, and the like. In 2009, 82.3 percent of Coloradans said they’d been physically active within the last month, according to a survey from the Centers for Disease Control and Prevention. The median for all states was 76.2 percent. Colorado is also tied with Oregon for 49th place in physical inactivity among adults. State health department officials suggest that Colorado’s hiking and fitness culture could draw trim and sporty types to move there, in which case lanky carpetbaggers might be helping to keep obesity rates down.

Demographically, the state had a lot going for it. We know that poverty and obesity are strongly correlated, and that people with more education are less likely to be obese. In 2008, 13.2 percent of Americans were living below the poverty line. In Colorado, that number was 11.4 percent, or 18th-best in the nation. According to the Lumina Foundation for Education, in that same year 37.9 percent of Americans between the ages of 25 and 64 held a college degree or higher, but in Colorado that number was 45.3 percent. (Only Connecticut, Massachusetts, and New Hampshire—all of which are thinner than average—rank higher in college degrees.)

Colorado has been the least obese state in the nation since at least 1995. In that year, the median obesity rate for all the states plus the District of Columbia was 15.9 percent; Colorado’s obesity rate was 10.1 percent. In 2009, the median for all states was 26.9 percent, and Colorado’s rate was 19.1 percent. So while Colorado remains the skinniest state, its obesity rate has nearly doubled in just a decade and a half. Furthermore, as of 2007, Colorado ranked near the middle on childhood obesity rates, so the nation’s girth map may soon be changing.

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Explainer thanks Eric Aakko of the Colorado Department of Public Health and Environment, Heidi Blanck and Kirsten Grimm of the Centers for Disease Control and Prevention, and Laura Segal of Trust for America’s Health.

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