The stunning three-decade rise in childhood obesity that prompted the government to declare an "epidemic" of fat appears to have leveled off, although the rate is still more than three times higher than in the 1970s, researchers reported Tuesday.
An analysis, based on data from tens of thousands of children, showed that the percentage of obese youngsters has been roughly stable since 1999 in every age and racial group surveyed.
The level of obesity "is still too high," said lead author Cynthia Ogden, an epidemiologist with the federal Centers for Disease Control and Prevention. But she added, "Maybe there is some cause for optimism."
The mystery is what caused the plateau. The leading possibility is that educational and regulatory campaigns to get children to eat less junk food and exercise more have begun to pay off.
The findings "may signal that this national epidemic is not an unstoppable force," said Dr. Risa Lavizzo-Mourey, president of the Robert Wood Johnson Foundation, which has committed $500 million to promoting physical activity in communities and improving nutrition in schools.
"When parents, government, schools, the food and beverage industries, other businesses, and the nonprofit and philanthropic sectors work together, we can make progress, and we can reverse this epidemic," she said in a statement.
But some researchers said the answer could be that the epidemic has simply reached a saturation point -- children just can't get any fatter.
"Eventually, it had to level off," said S. Jay Olshansky, an epidemiologist at the University of Illinois at Chicago who was not involved in the study. "The question was when. Maybe this is it."
The rise in obesity among children and adults has been one of the biggest public health issues of the last few years, both in this country and around the world.
It was first noticed by researchers in the 1980s as a relentless upward slope that threatened to undo progress on heart disease and exacerbate other killer illnesses influenced by weight, including diabetes, high blood pressure and some types of cancer.
An unsettling report issued by the CDC in 2004 concluded that obesity caused 400,000 deaths a year in the United States, just slightly below the death toll from smoking.
About a third of U.S. adults are obese, based on a measurement known as body mass index, a ratio of height to weight.
Of particular concern has been obesity in children, because their eating patterns set them on course for lifelong health problems. One study in 2005 found that as a result of obesity, children today could be the first generation of the modern era to live shorter lives than their parents.
The most recent study, published in the Journal of the American Medical Assn., showed that 16.3% of children between the ages of 2 and 19 were obese and an additional 15.6% were overweight.
The government has been tracking the heights and weights of children since the 1970s as part of an ongoing health and nutrition survey. By today's definition, 5% of children at that time were obese and 10% were overweight.
The latest analysis, which looked at 4,207 children surveyed in 2005 and 2006, found that their body mass index ratings did not differ significantly from those of children surveyed in 2003 and 2004.
When the researchers incorporated the new numbers into their analysis, their statistical model showed that 1999 marked the beginning of the leveling off. The finding tracks with a study last year showing a stabilization of obesity rates among adults.
While the plateau in childhood obesity occurred among all races, the data highlighted continuing racial disparities.
For example, the study found that among girls ages 12 to 19, nearly 27.7% of blacks and 19.9% of Mexican Americans were obese, compared with 14.5% of whites. Among boys ages 6 to 11, 27.5% of Mexican Americans and 18.6% of blacks were super-obese, compared with 15.5% of whites. Data on Asian children were not presented in the study.
Dr. William Dietz, a CDC child obesity expert who was not involved in the study, said that despite the continuing disparities, the overall trend showed that widespread efforts to change the behavior of children might be working.
"I'm hopeful," he said. "We haven't turned the corner, but we may be at the corner."
That could represent a tremendous victory for public health, given the complexity of obesity. In the last several years, some schools have eliminated soda machines, media coverage of obesity has proliferated, and even fast-food restaurants have introduced low-fat meals.
Obesity rates are driven by a complicated mix of factors, starting with genetic susceptibility and the eating habits of mothers during pregnancy.
Layered over that are economic and cultural trends, including falling food prices, the increased marketing of junk food and the increasing time children spend watching TV and playing electronic games instead of exercising.