After a 30-year, record-shattering rise, U.S. obesity rates appear to be stabilizing.
New statistics cited in two papers report only a slight uptick since 2005 — leaving public health experts tentatively optimistic that they may be gaining some ground in their efforts to slim down the nation.
Many obesity specialists say the new data, from the Centers for Disease Control and Prevention, are a sign that efforts to address the obesity problem — such as placing nutritional information on food packaging and revising school lunch menus — are beginning to have an effect in a country where two-thirds of adults and one-third of children and teens are overweight or obese.
"A good first step is to stop the increase, so I think this is very positive news," said James O. Hill, director of the Center for Human Nutrition at the University of Colorado Health Sciences Center in Denver. "It may suggest our efforts are starting to make a difference. The bad news is we still have obesity rates that are just astronomical."
Historically, there was little change in Americans' sizes from 1960 through 1980. But obesity rates soared through the end of the century, for reasons that are still debated.
The new studies reflect 2009-10 data, the most recent available, from the government's National Health and Nutrition Examination Survey, which examined 6,000 adults and 4,111 children, measuring their body mass index, among other items. Though a number of organizations measure obesity rates, the survey's data are considered among the most accurate.
The statistics showed that more than 35% of U.S. adults (78 million people) are obese, defined as having a body mass index of 30 or greater. That is similar to the 2005-06 rate. Calculated as weight in kilograms divided by height in meters squared, the BMI is not a perfect measure of fatness but is still viewed as the gold standard in assessing population-wide trends.
An additional third of adults are overweight, the analysis found, also similar to the rates in 2005-06.
Likewise, data in children and teenagers from birth to age 19 reflect little change from the survey's 2007-08 data, according to the reports, which were published online Tuesday in the Journal of the American Medical Assn. Almost 17% are obese and 32% are overweight or obese.
But though obesity rates may be flattening overall, increases and disparities can still be found in specific racial and ethnic groups.
Rates have risen to 58.5% among non-Hispanic black women and to nearly 45% among Mexican American women since 2004, for example. And among children and teens, about 21% of Hispanics and 24% of blacks are obese compared with 14% of non-Hispanic whites.
The report also found that gender differences appear to be fading, with percentages of overweight males catching up with or even overtaking those of females.
Among males under 19, obesity rose from 14% in 1999-2000 to 18.6% in the latest survey; in adult men, the rate jumped from 27.5% to 35.5%.
In addition, more adult men are now overweight or obese as compared with women — 73.9% to 63.7%. Severe obesity remains more common in women, however.
"We found no indication that the prevalence of obesity is declining in any group," the authors wrote in one of the papers, which looked at obesity rates among adults.
It's not clear why obesity rates are still rising in some groups while stabilizing in others, said Cynthia L. Ogden, a coauthor of the two papers and a researcher at the CDC. But the best bet of some leading obesity experts is that obesity prevention initiatives in some pockets of the country are paying off.
The Let's Move! program founded by First Lady Michelle Obama has raised national awareness through actions such as persuading Wal-Mart to stock more healthful foods and working with professional sports organizations to create public service announcements encouraging children to exercise.
Certain states, including California, have made obesity prevention a major health goal through measures to reduce access to sugary drinks and high-calorie, unhealthful snacks in schools.
A UCLA study released in November showed obesity rates ticking down in some parts of the state between 2005 and 2010, including a decline of 2.5% in Los Angeles County. And research published last month found obesity rates in New York City children fell 5% between the 2006-07 and 2010-11 school years.
"The places that are making serious changes in the schools and communities can take hope that these changes are starting to have an effect," said Dr. James S. Marks, senior vice president and director of the health group for the Robert Wood Johnson Foundation, a private organization aimed at improving health of Americans.
But, he added, a reduction in obesity rates will probably take many more years and more than the smattering of programs and initiatives so far underway.
The best hope for lowering rates, he said, is to stop people from getting fat to begin with: Experience and studies show that it is difficult for obese adults to permanently shed fat and that children who are already overweight or obese are highly likely to be overweight as adults.
Only one prescription anti-obesity medication is currently approved for long-term use, and researchers have stalled in their efforts to find more. Moreover, most obesity is untreated or under-treated.
Since obesity contributes to joint damage as well as diseases such as diabetes, heart disease and certain cancers, the epidemic truly is a national crisis, said Patrick M. O'Neil, president of the Obesity Society and director of the weight management center at the Medical University of South Carolina in Charleston.
"Even if the statistics stay at current prevalence rates, I see little good news in that," O'Neil said.
People should look to their own lives and individual experiences, and strive for progress by eating more healthfully and exercising more, he said.
"On a population basis you are trying to turn an aircraft carrier, and it's going to take a long time for it to change," he said.