Washington ? It may be the malady of the month, but there’s no getting around the fact that Americans are obese. Not all of us, of course, but a troublesome percentage of the population. And the numbers keep rising.

This may seem like a paradox, since more Americans than ever are joining health clubs or working out in the company gym, jogging every day and competing in an ever-increasing calendar of marathons. Every parent of an adolescent girl (or boy, for that matter) has reason to worry about anorexia or bulimia, and supermodels are skinnier than ever. Your grocery store has a section devoted exclusively to diet foods, and the aisles feature products such as low-fat Oreo cookies.

Or look at it another way. A generation or two ago, there was malnutrition in the land, and instead of articles on obese Americans, the press was full of stories about pellagra in Kentucky or, as Franklin Roosevelt put it in his Second Inaugural, “I see one-third of a nation ill-housed, ill-clad, ill-nourished.” In the good old days, the rich were fat and the poor were lean; now it’s the other way around. We have progressed far enough, and grown so affluent, that even impoverished Americans have grown voluminous on a diet of fats, carbohydrates, sugars and cheese balls.

There are two culprits, obviously. One is prosperity. It is not for nothing that we are the world’s wealthiest society: America’s poverty line is a comfortable lifestyle in most parts of the world. Generally speaking, Americans no longer worry about their next meal: Food is cheap, ubiquitous, available in unlimited quantity and variety, and the average — even the well-below-average — household income is sufficient to keep it plentiful.

The other culprit is material progress. Fewer and fewer Americans engage in manual labor, or work with their backs; the only sweat they generate on the job is due to anxiety, not activity. At home, Americans no longer shovel coal for heat, sweep their floors with a broom, chop wood for fire, hang a clothesline, walk to concerts or (in my neighborhood, at least) do their own gardening. The combination of electricity, asphalt highways and automobiles, radio/TV and now computers has made sitting the national imperative.

So long as people can afford to drive to the office, sleep with air-conditioning and surf the Internet, they are likely to do so. And who can blame them? The answer, therefore, is not revolution but (in the best Darwinian sense) adaptation. For obesity is not just unsightly, it is lethal and dramatically shortens our comfortable existence.

Comes now the American Council for Fitness and Nutrition, a consortium of food, beverage and consumer-products companies, nonprofits and trade associations, to suggest solutions based on medical knowledge, human nature and common sense. The key, says the ACFN, is not a lifetime of crash diets or a sequence of 10-mile “fun” runs; the key is achieving a balance of intelligent diet and routine physical activity in our daily lives.

The old ideal remains the wiser system: to restrict our intake of food to prudent levels, keeping Whoppers and banana splits to a minimum, and to integrate physical activity into each day. This does not necessarily mean grunting for washboard abs at the gym, but a daily brisk 10-minute walk, mowing the lawn, shoveling snow, playing catch, climbing the staircase instead of taking the elevator.

Of particular interest to the council is the waistline of American youth. The number of children enrolled in physical-education classes is on the decline, and only one state, Illinois, mandates daily physical activity for students through high school. The public schools, in particular, are vulnerable to mandates for political correctness. How much better it would be — for them and for the national well-being — if students learned the rudiments of sound nutrition, the elements of a healthy diet, the obvious connection between a balanced program of moderate nourishment and exercise and good health and increased longevity.

Philip Terzian is the associate editor of the Providence Journal.