Our Waistlines Are Expanding In Sync With Our Car-Dependence

States with the highest obesity rates also tend to be where the fewest people bike or walk to work. Image: CDC

Two
reports released last week underscored the increasing severity of
America's obesity epidemic. And the eye-opening findings add to the
mounting evidence that stopping the spread of obesity and its attendant
health risks will require changes to the nation’s transportation system
as surely as it demands altering our diets.

A report from the Centers for Disease Control and Prevention released Tuesday
showed the number of obese Americans has increased by 2.4 million since
2007. There are now nine states where more than 30 percent of the
population qualifies as obese -- up from three states in 2007. (Just ten
years ago, no state had obesity levels above 30 percent). 

The following day, Gallup released a ranking
of the nation’s most and least obese states as part of a broader index
of well-being. By its accounting, a cluster of states in the southeast
-- West Virginia, Kentucky, Mississippi, Arkansas, and South Carolina --
have the highest rates of obesity, while the thinnest states, mainly in
the west and New England, tend to have obesity rates about ten
percentage points lower.

In the CDC ranking of states (which varies slightly from the Gallup
ranking), Colorado and the District of Columbia are the only states
with obesity rates under 20 percent, making their rate nearly 15 points
lower than the most obese states. Their secret? During a press briefing, the CDC's Bill Dietz speculated
that Colorado’s investment in biking and walking trails, as well as
District residents' frequent use of public transportation, which goes
hand in hand with walking and thus burns more calories than driving, are
possible factors.

Indeed, if you look at rates of active commuting (walking and
biking) in the most and least obese states, a revealing correlation
emerges. Three of the five most obese states in the Gallup ranking are
also among the five states with the smallest percentage of people who
bike to work. At the other end of the spectrum, four of the ten thinnest
states are among those where people bike to work most frequently. (The
commuting rates come from Census data detailed in this League of American Bicyclists report.)

The relationship seems to hold up when you include walking. People
in the five most obese states make about 5.2 percent of all trips by
bike or on foot, according to data published recently in a 2010 benchmarking report
from the Alliance for Biking and Walking. In contrast, people in the
five least obese states made twice as many trips -- 10.2 percent of them
-- by bike or on foot. 

It seems unlikely that you can chalk this all up to coincidence,
but it's worth noting that these are back-of-the-envelope comparisons
made without the eye of a trained statistician. And, as Dietz noted in
the press briefing, other factors (such as demographic differences)
surely play an important role.

For a second opinion, I checked with John Pucher,
a Rutgers University planning professor with ample experience crunching
these sorts of numbers. The relationship between a lack of active
commuting and obesity is absolutely real, Pucher said via email. In
fact, Pucher and colleagues have just completed a rigorous study of the
relationship in which they examined health and travel data for 14
countries, all 50 U.S. states, and 47 of the 50 largest American cities.

At all three levels, the researchers found a clear negative
relationship between active travel and obesity. Differences in
transportation choices account for nearly a third of the variation in
obesity rate among states, their analysis shows. Since the study hasn't
been published officially, Pucher couldn't reveal any more specifics at this time. But stay tuned: The full study will come out in the American Journal of Public Health on August 20, and we'll have more details then.