After 25 years of what health officials call an obesity epidemic, American adults finally may be getting a handle on the battle of the bulge, according to federal data released Wednesday.
The Centers for Disease Control and Prevention said 34.3% of adults -- or more than 72 million people -- were obese in 2005 and 2006. The figures were essentially unchanged from the previous two-year period for the first time since 1980.
Merely halting the rise in obesity may seem a modest accomplishment, especially with the number of overweight Americans idling at an all-time high.
But in comparison to a quarter-century of expanding waistlines that doubled the proportion of Americans considered obese, some experts called the study a tentative milestone.
"It is great that the problem is not increasing," said Meir Stampfer, a professor of nutrition and epidemiology at the Harvard School of Public Health. But he added: "This does not mean that the problem is over."
The report didn't weigh in on why Americans seem to be holding steady. Experts surmised that the government's incessant calls for people to slim down may be finally paying off. They added that membership in fitness clubs is on the rise, and prohibitions against artery-clogging trans fats in restaurants are gaining ground in the name of public health.
Others raised a more fundamental explanation.
Glenn Gaesser, an exercise physiologist at the University of Virginia and author of the iconoclastic book "Big Fat Lies," said there just may be metabolic limit to body weight.
Americans may have finally reached that point. "You can only get so fat," he said
Obesity is defined as having a body-mass index -- a mathematical formula of the ratio of weight and height -- of 30 or more. A woman who is 5 feet tall would be considered obese if she weighed at least 154 pounds. A 6-foot-tall man would be obese if his weight topped 220 pounds.
Turning back the remarkable rise of obesity has been one of the great public health challenges of recent times.
Health officials have long nagged the public over its bad habits: bigger portion sizes, eating more meals in restaurants, sedentary lifestyles, and an increasing proclivity for automobiles over walking. Not only have more adults become obese, but those who are weigh more than ever.
The problem is not just aesthetic. People who are obese are more likely to suffer from diabetes, cardiovascular disease, high blood pressure and some types of cancer. Obesity is also associated with an increased risk of overall disability and of death from any cause. The more one weighs, the higher the risk.
In 2004, the CDC issued an alarming report that said the nation logs 400,000 deaths a year due to obesity, just slightly below the 435,000 who die from smoking.
Federal health guidelines set by the Department of Health and Human Services call for the nationwide obesity rate to drop to 15% by 2010 -- a level not seen since the early 1970s.
The latest report is based on data from a CDC project called the National Health and Nutrition Examination Survey, which combines interviews with physical examinations and is conducted every two years.
The latest round of data found that the obesity rate remains slightly higher among women, at 35.3%, but that figure has stabilized since 1999, said Cynthia Ogden, the CDC epidemiologist in Washington who led the study. The rate for men was lower at 33.3%, but it is not yet clear whether they have reached a plateau as well, she said.
Middle-age adults are still packing on the most pounds. The study found that 53% of non-Latino black women and 51% of Mexican American women between the ages of 40 and 59 were classified as obese, compared to 39% of non-Latino white women.
After age 60, the obesity rate for black women jumped to 61%, though it declined to 37% for Mexican American women and to 32% among non-Latino white women, according to the report.
The study didn't include enough people from other racial and ethnic categories to calculate rates for other groups, Ogden said.
Among men, obesity rates were also highest for those in their 40s and 50s. However, the researchers did not find significant differences between racial and ethnic groups. The researchers don't know why men and women differ in that regard, Ogden said.
They also don't know why overall obesity rates decline after age 60. Illnesses and natural changes in metabolism could be contributing factors, she said.
Ogden cautioned that more data are needed to determine whether the overall obesity epidemic has stalled or the new figures represent a temporary lull.
Even if the trend holds, it "does not mean the problem has gone away," said Jeffrey M. Friedman, a molecular geneticist at Rockefeller University in New York. "A significant proportion of the population is obese."
Some say the report calls into question the existence of an obesity epidemic in the first place. They said the data support the notion that obesity has a strong genetic component and does not simply result from a bounty of fatty or sugary foods.
"All the people with obesity-susceptible genes have reached their maximum potential in terms of weight, and the people who are naturally thin are not obese and are not going to become obese," said Paul Ernsberger, a nutritionist at Case Western Reserve University in Cleveland who has developed a genetic model of obesity in rats.
Increasing rates of childhood obesity leave some skeptical that obesity rates among adults will be able to hold steady, let alone fall.
Gary D. Foster, director of the Center for Obesity Research and Education at Temple University in Philadelphia, noted that the rate of childhood obesity had risen from 5% to 17% over the last couple of decades.
"Knowing what we know about the natural course of body weight from childhood to adulthood," he said, "you would expect that the rate of adult obesity will increase."
But Stampfer of Harvard said the trend may reflect an earlier onset of obesity, not an increase in the number of people prone to gaining weight.
Still, adults who have been obese since childhood will probably also develop diabetes, hypertension and other health problems at a younger age, he said.