Almost nobody knows who  or even what  the surgeon general is, so almost nobody noticed when David Satcher’s term in that office recently expired. But notice what he did when stepping out the door. His warning about obesity, properly amplified, may demonstrate why the office of surgeon general sometimes is the government’s most cost-effective institution.

In this mostly middle-class, broadly educated, information-acquiring country, often the most effective dollars government spends pay for the dissemination of public health information. In an affluent society, which has banished scarcity and presents a rich range of choice, many public health problems are optional  the consequences of choices known to be foolish.

Imagine how America’s health profile would be improved by substantial reductions in coronary artery disease, lung cancer, AIDS, violence and vehicular accidents. All five are often results of behavior known to be risky. Now imagine Americans take to heart, so to speak, Satcher’s warning that obesity may soon surpass smoking as the nation’s principal cause of preventable death.

Although Americans spend more than $30 billion a year on weight-loss products or programs, obesity is, strictly speaking, epidemic. Scientists for the Centers for Disease Control and Prevention reported that in 1991 only four states had obesity rates of 15 percent or higher. Today 37 do and the obesity rate is increasing in every state and among all racial and ethnic groups. “Rarely,” the report says, “do chronic conditions such as obesity spread with the speed and dispersion characteristic of a communicable disease.”

A quarter of all Americans smoke (down from half in the two generations since the 1964 surgeon general’s report connecting smoking with cancer). But most American adults  61 percent  are overweight or obese, primarily because they eat imprudently and exercise negligibly. Smoking-related illnesses kill 400,000 a year, but illnesses related to obesity  heart attacks, strokes, diabetes, some cancers  kill 300,000, are increasing faster than smoking-related illnesses and threaten to nullify recent gains made against those illnesses.

Unlike cigarettes, french fries  America’s annual per capita consumption: 28 pounds  are neither addictive nor harmful when enjoyed in moderation. And public health information encourages moderation. But if you want to buy a weight-loss product, almost any bookstore has Eric Schlosser’s best-selling “Fast Food Nation: The Dark Side of the All-American Meal.” It is a sure-fire appetite-suppressant.

Like a lot of people hell-bent on forcing root-and-branch reform of society, Schlosser’s zealotry approaches monomania: He traces an amazing number of social ills to fast food. However, even allowing for the fact that fewer than one-third of Americans bestir themselves to get the medically recommended minimum amount of exercise, Schlosser plausibly argues this: There is more than coincidence in the correlation of the increase of obesity and the rise of the fast- food industry.

“What we eat,” he writes, “has changed more in the last forty years than in the previous forty-thousand.” He says half the money Americans spend on food  more than on higher education or new cars  is spent at restaurants, mostly at the fast-food sort. On any given day, a quarter of America’s adults visit such restaurants. Every month 90 percent of children aged 3 to 9 visit a McDonald’s. Commodity prices have fallen, so serving sizes have risen. McDonald’s largest serving of french fries is three times larger than it was a generation ago. In the late 1950s the typical fast-food restaurant soft drink was eight ounces. Today McDonald’s “large” Coke is 32 ounces  and 310 calories.

Now, food fascists are among the most annoying killjoys in our midst. They are immoderate in their animus against foods which are harmless pleasures if they are not a steady diet. But before tucking into your next double cheeseburger with bacon (70 percent of bacon sold in America is on fast food), calculate your BMI Â Body Mass Index.

Divide your weight in pounds by the square of your height in inches, then multiply by 703. If the resulting number is below 25 you are not overweight. If it is 25 to 29 you, like 34 percent of Americans aged 20 to 74, are overweight. Since 1970 the percentage of children aged 6 to 11 who are overweight has almost doubled, from 7 to 13. The percentage for adolescents aged 12 to 19 has almost tripled, from 5 to 14, which may have something to do with the fact that for at least 2 hours a day 43 percent of people in grades nine through 12 are immobile, watching television.

If your BMI number is 30 or higher you, like 27 percent of adults, have supersized yourself. You are obese. Bon appetit.

 George Will is a columnist for Washington Post Writers Group.