Two recent studies on obesity tell us we need to make healthy choices, and one of these studies reported in The Economist discusses what it calls “a striking relationship” between obesity and driving.

The Economist says Americans are getting fatter: obesity rates have risen 74% in the past 15 years to nearly 28% of the adult population. And they are driving more: the number of vehicle miles traveled by each licensed driver (VMT/LD), excluding commercial vehicles, increased by an average of 0.6% a year between 1988 and 2008.

Academics at the University of Illinois say there’s a striking correlation between these two variables—but with a large time lag. They noted that previous research had found that changes in diet had an effect on body weight only after some six years. Therefore VMT/LD in 2004 is correlated with obesity in 2010.

This near-perfect correlation (99.6%) permits predictions about obesity rates. Since VMT/LD fell in 2007 and 2008, America's obesity rate could fall to as low as 24% in 2014. These predictions come with a strong caveat: correlation does not equal causation. And the authors said they did not control for factors such as diet, income and lifestyle. Additionally, they did not explore the possibility that the larger, and thus more immobile people become, the more they drive.

A second report produced by the Trust For America’s Health and the Robert Wood Johnson Foundation, based on a three-year study by the U.S. Centers for Disease Control, identifies the states with the highest rate of adult obesity rankings: Mississippi (33.8%); Alabama (31.6%); Tennessee (31.6%); West Virginia (31.3%); and Louisiana (31.2%). The states with the lowest rate of adult obesity are as follows: Colorado (19.1%); Connecticut (21.4%); District of Columbia (21.5%); Massachusetts (21.7%); Hawaii (22.6%) and Vermont (22.8%) (For the complete listing, visit Healthy Americans.

What does all this mean? We want better fuel economy and that often means smaller vehicles. But, as a society too many of us are getting too large. What will change first, our vehicles or us?