Obesity is considered a major public-health problem, but many scientists are coming to see it as a comparative blessing, given the alternative. These public-heath experts believe...

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Obesity is considered a major public-health problem, but many scientists are coming to see it as a comparative blessing, given the alternative. These public-heath experts believe, in effect, that America may have traded smoking — a truly lethal habit — for the lesser deadliness of eating too much.

The story of this trade-off can be seen in the data. From 1973 until 1983, Americans actually were growing thinner. During that period, the average weight of middle-aged men fell about 2 pounds, while that of middle-aged women fell nearly 3 pounds.

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The trend then reversed: From 1980 to 2000, the average weight of Americans rose by nearly 20 pounds. Everyone got heavier, said Dr. David Williamson, a statistician at the Centers for Disease Control and Prevention (CDC). “Competitive cyclists weigh more than they did 20, 30 years ago; HIV patients weigh more.”

Yet the nation also is healthier. Life expectancy has gone up by more than six years over the past three decades, and heart disease, long the major killer, is on the wane.

A big reason Americans are fatter and healthier, Williamson believes, may be the steep decline in cigarette smoking.

If he is correct, the increase in obesity is a classic case of unintended consequences — one of a long list of medical and public-health interventions whose full effects could not be foreseen.

For example, Americans once died in great numbers in infancy, or childhood, and women died in childbirth from infectious diseases. Now they don’t — a triumph of public health. But as a consequence, the population is growing ever older, which in turn is creating a host of profound public-health challenges.

“We’re just now trying to deal with the medical consequences” of an aging nation, Williamson said.

The connection between smoking and obesity is not proven, but the statistical correlations are there. From 1980 to 2000 — as body weight was rising — smoking rates fell by 27 percent in the nation as a whole and by 38 percent among middle-aged Americans. (Smoking rates have leveled off, Williamson notes, and there are signs that obesity rates are leveling off, too.)

“There is no question that smoking affects the epidemic” of obesity, said Dr. Neil Grunberg, a psychologist and neuroscientist at the Uniformed Services University of the Health Sciences in Bethesda, Md.

Smokers who quit, he noted, gain about 10 to 12 pounds on average, in part because they crave sweet foods and carbohydrates. In addition, Grunberg said, smokers’ metabolism slows after they quit.

Dr. Michael Grossman, an economist, and his colleagues at the Graduate Center of the City University of New York have analyzed the economic causes of obesity. They have calculated, based on cigarette-tax receipts, that for every 10 percent increase in the price of cigarettes, the number of obese people increases 2 percent. Smoking cessation, they estimate, accounted for 20 percent of the obesity increase in this country.

Effect may be even bigger

Dr. Katherine Flegal, a statistician at the National Center for Health Statistics, said the effect may be even bigger, once scientists add the upward effect on average weight of the growth in the number of Americans who, because of the success of the anti-smoking movement, never smoked in the first place.

One possible explanation, Williamson said, is that as the number of smokers started to plummet, the demand for calories went up and the food industry began offering and advertising larger portions and more snack foods. “The food industry in general subconsciously picked up on this and went to town,” he said. Overeating soon became the norm, for everyone, even children.

Over the same period, said Dr. David Musto, a historian of science at Yale, America’s preoccupation with healthy foods — oat bran, broccoli, fish, etc. — also resulted in what he called a “barrage” of pro-eating commercial messages.

Health quest adds calories

In the 1960s, Musto said, it was socially imperative to smoke. “A man had to know his brand” of cigarettes, he said. In much the same way, he said, it became socially imperative to eat the right foods — those supposed to be good for you.

“The process of becoming obese is greatly facilitated by a search for health and healthy foods,” Musto said. “You’ve read that something fights Alzheimer’s or lowers your blood pressure, so why shouldn’t you have a healthy portion?”

It all makes for an odd and not entirely satisfactory coda to the anti-smoking crusade. But on balance, Williamson noted, a nation with an expanding waistline is in far better shape than one with a cigarette in its mouth. Obesity may be bad, he said, but the health effects of smoking are far worse.

“I sure would like for people not to be obese,” Williamson said. But, he added, if they got that way because they don’t smoke, then “maybe the sky isn’t falling quite as much as we think it is.”