And you thought it was mom's chocolate-chip cookies.
A new National Bureau of Economic Research working paper posits that economic factors—such as the cost of food and the type of jobs in your state—can affect weight gain. These variables, controlled for demographics, explain 37 percent of the increase in Body Mass Index in the U.S. from 1990 to 2010, as well as 59 percent of the rise in severe obesity, the paper finds.
Save Money. Live Fatter. The No. 1 reason we've gained weight? Wal-Mart.
To be fair, that's a massive oversimplification. People weighed more when the cost of calories decreased—that explained 36.5 percent of total BMI gains. The proliferation of supercenters and warehouse clubs was the biggest contributor to that trend, explaining 17.2 percent of weight gain.
There's a sad twist in this story. "Supercenter/warehouse club density increases the probability of weight-loss attempts," the authors find. Those efforts clearly went the way of your New Year's resolution, "raising the possibility that cheap food from these retailers triggers self-control problems."
Wal-Mart's Tara Greco, director of sustainability communications, said in an e-mail that the company has committed to using its business and philanthropic resources to make healthier eating easier in the U.S. The chain is in the process of reducing sugars and sodium, and eliminating industrially produced trans fats, in products carried in its stores, she said.
Additional economic changes that make Americans pack on the pounds include rising cigarette prices, more restaurants, and fewer blue-collar jobs.
There is Hope. And it lies in your local treadmill. Fitness-center expansion and increases in gas prices were shown to correlate with lower BMI's.
The take-away? When it comes to expanding waistlines, the economic conditions you live in matter. A lot. That's important because the adult obesity rate in the U.S. jumped from 13 percent in 1960 to about 35 percent by 2012.
The paper was written by Georgia State University's Charles Courtemanche, the University of Louisville's Joshua Pinkston, Christopher Ruhm of the University of Virginia, and the University of Iowa's George Wehby.