“I don’t think the campaign will have any positive effect. Now if you did this in the United States, there would be benefits, since there are many Americans who weigh more than 100 kilograms,” or about 220 pounds, Mr. Ogushi said. “But the Japanese are so slender that they can’t afford to lose weight.”

Image A poster at a public health clinic in Japan reads, "Goodbye, metabo," a word associated with being overweight. The Japanese government is mounting an ambitious weight-loss campaign. Credit... Ko Sasaki for The New York Times

Mr. Ogushi was actually a little harder on Americans than they deserved. A survey by the National Center for Health Statistics found that the average waist size for Caucasian American men was 39 inches, a full inch lower than the 40-inch threshold established by the International Diabetes Federation. American women did not fare as well, with an average waist size of 36.5 inches, about two inches above their threshold of 34.6 inches. The differences in thresholds reflected variations in height and body type from Japanese men and women.

Comparable figures for the Japanese are sketchy since waistlines have not been measured officially in the past. But private research on thousands of Japanese indicates that the average male waistline falls just below the new government limit.

That fact, widely reported in the media, has heightened the anxiety in the nation’s health clinics.

In Amagasaki, a city in western Japan, officials have moved aggressively to measure waistlines in what the government calls special checkups. The city had to measure at least 65 percent of the 40- to 74-year-olds covered by public health insurance, an “extremely difficult” goal, acknowledged Midori Noguchi, a city official.

When his turn came, Mr. Nogiri, the flower shop owner, entered a booth where he bared his midriff, exposing a flat stomach with barely discernible love handles. A nurse wrapped a tape measure around his waist across his belly button: 33.6 inches, or 0.1 inch over the limit.

“Strikeout,” he said, defeat spreading across his face.

The campaign started a couple of years ago when the Health Ministry began beating the drums for a medical condition that few Japanese had ever heard of  metabolic syndrome  a collection of factors that heighten the risk of developing vascular disease and diabetes. Those include abdominal obesity, high blood pressure and high levels of blood glucose and cholesterol. In no time, the scary-sounding condition was popularly shortened to the funny-sounding metabo, and it has become the nation’s shorthand for overweight.