“The Economics of Obesity” by Inas Rashad and Michael Grossman, in The Public Interest (Summer 2004), 1112 16th St., N.W., Ste. 140, Washington, D.C. 20036.

Obesity was responsible for about 400,000 deaths in 2000, and is fast catching up with smoking (435,000 deaths) as the nation’s leading cause of preventable deaths. It turns out, though, that the two killers are working together in an unusual way.

After remaining steady for two decades, American obesity rates rose sharply between 1980 and 2000. The percentage of obese adults went from 14 to 30, and that of overweight children from five to 14. Genetics helps to explain an individual case of obesity but not the massive collective increase.

Economists have identified various causes, including a drop in food prices and the introduction of the microwave oven, which favors fattier foods. But the chief cause, responsible for up to two-thirds of the increase in adult obesity since 1980, say economists Rashad, of Georgia State University, and Grossman, of the City University of New York, is the explosive increase in the number of meals consumed outside the home, particularly fast food. And what’s the principal reason so many Americans are dining out so often? Women’s increased numbers in the labor force.

The next-most-powerful factor in promoting obesity, the authors note, is perhaps more surprising than the proliferation of restaurants: the war on smoking. Higher taxes on cigarettes, and the resultant higher prices, have prompted large numbers of smokers to quit. And once deprived of the appetite-suppressing effect of smoking, they eat more. Other things being equal, say Rashad and Grossman, a 10 percent increase in the inflation-adjusted price of cigarettes produces a two percent increase in the number of obese people. The authors calculate that the 164 percent increase in the price of cigarettes since 1980 is responsible for 20 percent of the national rise in obesity.

Rashad and Grossman don’t advocate that the overweight take up smoking, or that women quit their jobs to stay home and cook. But they do have a suggestion for the collective fight against fat: Perhaps the government should subsidize exercise programs and facilities for the obese. It might also work through schools and recreation centers to help children ward off those menacing extra pounds.