Why Have Americans Become More Obese?

Illustration of obesity and waist circumference. From left to right, as labeled in the original image, the "healthy" man has a 33 inch (84 cm) waist, the "overweight" man a 45 inch (114 cm) waist, and the "obese" man a 60 inch (152cm) waist.

If you want to understand obesity in America, and how it's changed in the last few decades, just take a look at the potato.

Americans have always eaten a lot of potatoes, but before the 1950s, people mostly baked, boiled, or mashed their spuds at home. Today the most common way Americans consume their favorite vegetable is the french fry—cut and peeled by a machine, frozen for transport, and then deep fried at a fast food chain.

In their essay, "Why Have Americans Become More Obese," three economists argue that the nature of obesity in the United States has shifted as a result of changes in how food is prepared: "The switch from individual to mass preparation lowered the time price of food consumption and led to increased quantity and variety of foods consumed." Faster preparation meant taking in more calories, leading predictably to an ever-expanding waistline.

David Cutler, Otto Eckstein Professor of Applied Economics, and Edward L. Glaeser, the Fred and Eleanor Glimp Professor of Economics, co-authored the study in 2003 with Harvard alumnus Jesse M. Shapiro, now a professor of economics at the University of Chicago Booth School of Business.