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.

The technical change theory has several implications, which we test empirically. First, increased caloric intake is largely a result of consuming more meals rather than more calories per meal. This is consistent with lower fixed costs of food preparation. Second, consumption of mass produced food has increased the most in the past two decades. Third, groups in the population that have had the most ability to take advantage of the technological changes have had the biggest increases in weight. Married women spent a large amount of time preparing food in 1970, while single men spent little. Obesity increased much more among married women. Finally, we show that obesity across countries is correlated with access to new food technologies and to processed food. Food and its delivery systems are among the most regulated areas of the economy. Some regulations are explicit; for example, the European Union has taken a strong stance against genetically engineered food, and Germany for many years had a Beer Purity Law. Other “regulations” are cultural, like Jose Bove’s crusade against McDonald’s in France. Countries with a greater degree of regulation that support traditional agriculture and delivery systems have lower rates of obesity.

While the medical profession deplores the increase in obesity, the standard economic view is that lower prices for any good-either monetary or time costs- expand the budget set and make people better off. But self-control issues complicate this interpretation. If people have difficulty controlling how much they eat, lowering the time costs of food consumption may exacerbate these problems.

Certainly, the $40–$100 billion spent annually on diets testifies to the self-control problems that many people face. In the last part of the paper, we consider the welfare implication of lower food production costs when individuals have selfcontrol problems. We will argue that for the vast majority of people, the price reductions in food preparation have led to welfare increases.

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David M. Cutler, Edward L. Glaeser and Jesse M. Shapiro