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.
