Why Have Americans Become More Obese?

In the early 1960s, the average American adult male weighed 168 pounds.

Today, he weighs nearly 180 pounds. Over the same time period, the average female adult weight rose from 143 pounds to over 155 pounds (U.S. Department of Health and Human Services, 1977, 1996). In the early 1970s, 14 percent of the population was classified as medically obese. Today, obesity rates are two times higher (Centers for Disease Control, 2003).

Weights have been rising in the United States throughout the twentieth century, but the rise in obesity since 1980 is fundamentally different from past changes. For most of the twentieth century, weights were below levels recommended for maximum longevity (Fogel, 1994), and the increase in weight represented an increase in health, not a decrease. Today, Americans are fatter than medical science recommends, and weights are still increasing. While many other countries have experienced significant increases in obesity, no other developed country is quite as heavy as the United States.

What explains this growth in obesity? Why is obesity higher in the United States than in any other developed country? The available evidence suggests that calories expended have not changed significantly since 1980, while calories consumed have risen markedly.

But these facts just push the puzzle back a step: why has there been an increase in calories consumed? We propose a theory based on the division of labor in food preparation. In the 1960s, the bulk of food preparation was done by families that cooked their own food and ate it at home. Since then, there has been a revolution in the mass preparation of food that is roughly comparable to the mass production revolution in manufactured goods that happened a century ago. Technological innovations-including vacuum packing, improved preservatives, deep freezing, artificial flavors and microwaves-have enabled food manufacturers to cook food centrally and ship it to consumers for rapid consumption. In 1965, a married women who didn't work spent over two hours per day cooking and cleaning up from meals. In 1995, the same tasks take less than half the time. The switch from individual to mass preparation lowered the time price of food consumption and led to increased quantity and variety of foods consumed.

Our theory is nicely illustrated by the potato. Before World War II, Americans ate massive amounts of potatoes, largely baked, boiled or mashed. They were generally consumed at home. French fries were rare, both at home and in restaurants, because the preparation of French fries requires significant peeling, cutting and cooking. Without expensive machinery, these activities take a lot of time. In the postwar period, a number of innovations allowed the centralization of French fry production. French fries are now typically peeled, cut and cooked in a few central locations using sophisticated new technologies. They are then frozen at '40 degrees and shipped to the point of consumption, where they are quickly reheated either in a deep fryer (in a fast food restaurant), in an oven or even a microwave (at home). Today, the French fry is the dominant form of potato and America's favorite vegetable. This change shows up in consumption data. From 1977 to 1995, total potato consumption increased by about 30 percent, accounted for almost exclusively by increased consumption of potato chips and French fries.