More than a third of U.S. adults and 17 percent of kids and teens are obese, rates that haven't changed much in a decade, researchers say.
Only preschool-age children show signs of a turnaround, with their obesity rates nearly halved in the same period, according to a new federal study published in the Journal of the American Medical Association.
"The rapid increase in obesity we saw in the '80s and '90s has definitely slowed," said epidemiologist Cynthia Ogden. "There's some glimmer of hope in the new data in relation to the 2 to 5 year olds."
Ogden, a branch chief at the National Center for Health Statistics in Rockville, Maryland, a division of the Centers for Disease Control and Prevention (CDC), is lead author of the new study.
Obesity rates among 2 to 5 year old Americans dropped from 13.9 percent to 8.4 percent between 2003 and 2012, her team reports.
Not all the news on the national state of weight was positive, however.
Though the overall obesity rate across all U.S. age groups has been stable since 2003, women 60 years and older have been growing fatter. Their rate of obesity rose from 31.5 percent to 38 percent over nine years, the study found.
Ogden and her colleagues used the annual National Health and Nutrition Examination Surveys to examine obesity trends in representative samples of Americans between the 2003 - 2004 survey year and 2011 - 2012.
The 5.5 percentage point drop in the obesity rate among 2 to 5 year olds mirrored decreases found among preschoolers in previous studies, the authors write.
A report published last year, for example, found that after doubling over 30 years, the obesity rate among low-income preschool children fell in 19 U.S. states and territories.
Nonetheless, more than two-thirds of American adults and nearly one-third of youth aged 2 to 19 years old fell into the overweight or obese categories in 2011 - 2012.
For adults, body mass index (BMI) - a measure of weight relative to height - defines obesity. A BMI above 25 is considered overweight, and BMI over 29.5, which is equivalent to a 5-foot, 4-inch adult weighing 174 pounds, is considered obese.
For children, BMI calculations also factor-in the weights of other kids in the same age group.
The report does not discuss reasons for the drop in preschool obesity or the rising obesity among older women.
"There's been a lot of attention in this country on obesity, but we've really focused on childhood obesity," said Lieutenant Commander Ashleigh May.
"We're on the right track it appears with young children, but we still have a lot of work to do," said May, an epidemiologist in the CDC's Obesity Prevention and Control branch in Atlanta who was not involved in the study.
Contributors to the downward trend among young children may include increases in breastfeeding, decreases in sugar consumption, a national program promoting exercise and another that now gives low-income children more fruits and vegetables, May said.
Dr. David Ludwig, a pediatrics and nutrition researcher at the Harvard School of Public Health in Boston, read the report as a sign of a possible tiny step forward in the fight against obesity.
"The key finding is that obesity prevalence throughout the U.S. population has not changed in the last decade and remains at historic highs," Ludwig said in an email.
He also cautioned that the decline in obesity rates among preschool kids could result from chance.
"Nevertheless, if real, the lower prevalence among young children would be an encouraging sign that national pediatric obesity prevention efforts - though still grossly inadequate - may be having some impact," he said.
Michael Jacobson, executive director of the Center for Science in the Public Interest, said he sees the report as a sign the obesity epidemic may have peaked.
Gains against obesity in preschool children may be attributable to a decline in soda consumption and to adding fruit and vegetables to the federal nutrition program for low-income children, he said.
But Jacobson, who was not involved in the study, pointed out longstanding disparities among ethnic groups that it reveals. A stunning 82 percent of African-American women and 77 percent of Hispanic women were overweight or obese, compared to 63 percent of white women, in 2011-2012, the report finds.
"That's a real health crisis," Jacobson said. "These numbers are crying out for some real action."