Senior Fellow Kevin A. Hassett

If you overindulged in turkey last Thursday, you're not alone. Research by the National Institutes of Health has found that, on average, people gain about a pound during the period between Thanksgiving and late February. Most of the increase occurs between Thanksgiving and New Year's. When participants in the study were checked again a year later, they had gained another 1.4 pounds.

While those increases may seem small, a slender 25-year-old who picks up a pound a year for 50 years will become an obese 75-year-old. Data from the National Health and Nutrition Examination Survey suggest that more and more Americans are following such a path.

American males in their 20s who weighed, on average, 163.9 pounds in 1960 were found to weigh 191.5 pounds 40 years later as they entered their 60s and 70s. Females in their 20s weighed on average 127.7 pounds in 1960, but ballooned to 164.7 pounds 40 years later.

The extent to which America is growing fat is mind boggling. One common measure of obesity is the "Body Mass Index," or BMI. According to the National Institutes of Health, a normal BMI is between 18.5 and 24.9. You're overweight if your BMI is between 25 and 29.9; if it's above 30, you are obese.

In 1960, 20-year-old males on average in the U.S. had a BMI of 24.3, putting them in the normal range. Today, they have an average BMI of 28.6, well into the overweight range.

Females fared worse. The 20-somethings of 1960 had a BMI of 22.2. By 2000, the average for this same group, now aged 60 to about 70, was 29.2.

Tom Brady Obese?

Granted, BMI is an imperfect measurement of obesity, since overly muscled individuals often fall into the overweight, or even obese, range. New England Patriots quarterback Tom Brady's BMI, for instance, would place him solidly in the overweight range. However, the average American is hardly Tom Brady, who is 6-foot, 4-inches tall and weighs 225 pounds.

These numbers can be hard to fathom, so a couple of simple examples will help put them in perspective. According to the National Institutes' BMI calculator, a 5-foot, 4-inch-tall woman would have to weigh about 170 pounds to match the most recent body mass averages. A typical man of 5-foot, 10 would have to weigh about 200 pounds.

This skyrocketing obesity is a serious problem. It has been statistically linked to numerous health problems, including heart disease and diabetes.

Fiscal Burden, Too

These health problems also create an enormous fiscal burden. Annual medical costs for obese individuals are approximately $1,000 more than for people with normal weight. A 2004 study by the Research Triangle Institute and the Centers for Disease Control and Prevention found that almost half of all obesity-related health-care costs are paid for by Medicare and Medicaid. In 2002, obese enrollees in Medicare accounted for a quarter of total spending, up from 9 percent in 1987.

This health burden is paid for by everyone. Society is engaging in a large transfer of resources from individuals who exercise and watch what they eat to those who, in many cases, do not.

The obesity epidemic is different from many other diseases, in that the decisions of each individual can influence the outcome. Many forms of cancer are just bad luck, since they can strike anybody. While there is surely a medical or genetic component to obesity, there's no way the biological makeup of Americans has changed that much in a half-century. Much of the increase in the nation's weight must be attributed to ordinary folks who lack the self-control to pursue a healthy lifestyle.

A "Fat" Tax?

So what should we do? In many ways, this problem is a classic "externality." People who don't control their weight impose a cost on those who do. Economists have long preached that a tax should be imposed in such circumstances. If carbon emissions cause global warming, government should impose a carbon tax. If overweight individuals impose costs on everyone else, then the government should tax fat.

While such a tax brings forth nightmarish visions of April 15 weigh-ins, many governments have already begun to pursue a tax-related strategy to combat obesity. Seventeen states and Washington, D.C., have laws imposing special taxes on junk food.

A fat tax, and junk-food taxes, are probably bad ideas, however. First, once one allows government to micromanage our lives with special taxes, who is to say where it would stop? Wine consumption in moderation is now supposed to be healthful; why not subsidize wine consumption and pay for it with a tax on red meat?

Twinkies vs. Chicken

Second, the National Institutes of Health holiday study suggests that a junk-food tax would be poorly targeted. It seems unlikely that junk food explains the holiday weight gain. It's far more probable that the massive holiday feasts do. And why should an individual who wants to eat a Twinkie in June be taxed for that choice, while an individual who eats a whole barbecued chicken is not?

The beauty of the NIH holiday study is that it suggests a simple solution that might be better than a tax. Most Americans don't want to gain weight, but do anyway. They probably don't understand that most of the weight they gain each year comes during the holidays. NIH researchers found that individuals who exercise even moderately during that period saw much smaller weight gains.

That means there's an easy way out. If you want to stay slim, you don't have to start the Atkins Diet or join a health club and slog away on the treadmill 12 months a year. All you need to do is exercise more between Thanksgiving and New Year's. If every American vowed to do that, the obesity epidemic could be contained. Spread the news.

Kevin A. Hassett is a senior fellow and director of economic policy studies at AEI.