The assessments, from the Centers for Disease Control and Prevention, are a welcome respite from the seemingly endless reports of Americans getting fatter and fatter. The latest of several to find an obesity plateau, they suggest that those earlier findings were not aberrations but that Americans may truly have turned a corner.
But it's not time to reach for the cookie jar yet. Though abundant messages about eating smaller portions and getting regular exercise may finally be registering, health experts say there's more to be done before the fattening trend is not merely halted but reversed -- more policy changes, community programs and support groups.
Americans are still among the chunkiest folks on the planet, with 68% of adults overweight or obese.
"This is not a cause for complacency or celebration," says Dr. William H. Dietz, director of the Division of Nutrition, Physical Activity and Obesity at the CDC, "but it is cause for modest optimism."
One of the new studies, both released online Wednesday in the Journal of the American Medical Assn., examined height and weight data in a nationally representative sample of 5,555 adult Americans collected in 2007 and 2008. In the sample, 33.8% of the subjects was obese.
Those numbers were compared to ones collected from 1999 to 2006 in a similar sample. Among women, obesity statistics remained fairly flat throughout the period encompassed by the two studies. Obesity rates among men rose slightly during the decade, but leveled off in the later years.
The second study examined nationally representative data on 3,281 children and teens ages 2 to 19, as well as 719 infants and toddlers. It found that obesity rates -- about 10% for infants and toddlers and 18% for adolescents and teens -- have also been fairly consistent over the last 10 years.
The one exception was the heaviest weight class for boys ages 6 to 19, whose numbers have risen.
Cynthia Ogden, an epidemiologist for the CDC's National Center for Health Statistics and lead author of the children's report, said the findings track with other reports, such as the Youth Risk Behavior Surveillance System, which saw a plateau among students in grades nine through 12 from 2005 to 2007.
"We're continuing to see slowing," Ogden said, "although the prevalence of obesity remains very high."
Obesity experts said they're not sure what's causing the slowdown.
Just as many factors contribute to making people fatter -- sedentary lifestyles; availability of inexpensive, fattening foods; and fewer walkable communities -- a comparable number could explain why our weight is now holding steady.
Dietz believes that an increasing consciousness of the crisis, coupled with copious public health messages and policies, may have contributed.
It's hard to have missed the admonitions in the last several years about choosing lower-fat foods, eating smaller portions and getting regular, moderate exercise. At the same time, more states and counties are providing healthier school lunches, banishing sugary sodas from campuses and passing laws to put nutritional information on restaurant menus.
However, Dietz said, "we don't know what people are doing differently" yet because it hasn't been measured.
Another theory about the plateau is that the population has gotten as fat as it's going to get -- that it has reached a kind of "fat set point."
"It's an interesting idea," albeit one that needs more research, Ogden said. She noted that similar plateaus have been observed in other countries but at different national rates of obesity.
Dr. Howard Eisenson, program director of the Duke Diet & Fitness Center in Durham, N.C., sees glimmers of hope in the studies but says the real challenge is to get people to exercise. "The survey only looks at BMI; it doesn't look at physical fitness, which doesn't get enough attention," he said. "Poor physical fitness is a matter of big concern."
The key to reversing the obesity trend may lie in preventing children from becoming overweight in the first place, said Dr. Thomas Robinson, professor of pediatrics at Stanford University and director of the Center for Healthy Weight at Stanford's Lucile Packard Children's Hospital.
"We have had more success in preventing obesity in children than we have in trying to treat obesity in adults," Robinson said. "Most [adults] regain the weight they lose."
Grass-roots movements in communities to get children active and teach them better nutrition have been effective, he added, but much more needs to be done.
"We've seen nothing with obesity that compares to how we've addressed the H1N1 flu in terms of the amount of resources and . . . effort," he said. "What the results call for is an even greater priority placed on the problem -- so that hopefully things will start to turn back."