Jan. 17, 2012 -- The growth in the nation’s obesity rate appears to be slowing and in some groups leveling off, according to new research. Yet, the rate is still more than double the government’s goal for 2010.

“This seems to be happening all over the world,” researcher Katherine Flegal, PhD, a senior research scientist at the CDC’s National Center for Health Statistics, says of the stabilization of the obesity rate among adults. Flegal and her colleagues published a report on adult obesity trends and a paper on obesity trends in children and teens in the Journal of the American Medical Association.

The proportion of obese U.S. adults changed little in the 1960s and 1970s, but grew nearly eight percentage points between the 1976-1980 and 1988-1994 National Health and Nutrition Examination Surveys, or NHANES.

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In 2009-2010, more than 35% of men and women and nearly 17% of children and teens aged 2-19 were obese, Flegal and her co-authors write. That adds up to a total of 90.5 million obese Americans. The Healthy People 2010 goals were 15% obesity among adults and 5% obesity among children.

Obesity in adults was defined by a body mass index, or BMI, of 30 or greater. BMI is a calculation based on an individual’s height and weight. For example, a 5-foot-4 adult falls into the obese category starting at 174 pounds, while a 5-foot-9 person is obese at 203 pounds or more. In children, obesity was defined as a BMI at or above the 95th percentile for the child’s age and sex.

Using NHANES data, the researchers compared obesity rates for 2009-2010 with those for 1999-2000. An increase was seen only in men and boys, but not in women and girls. In 2009-2010, women aged 60 and over were more likely than younger women to be obese, but there was no significant difference in prevalence of obesity in men by age.

Compared to white and Hispanic adult survey participants, obesity was most common in African-Americans, about half of whom had a BMI of 30 or greater. However, the authors note, “at a given BMI, black men and women tend to have higher lean mass and lower fat mass than white men and women.”

Similar racial/ethnic differences were found in children and teens aged 2 through 19, with about a quarter of African-Americans in that age group meeting the definition of obesity. As with adults, the researchers write, BMI “is an imperfect measure of body fat.”

“It is not clear, however, if body fatness is a stronger predictor of obesity-related health outcomes than is BMI,” the researchers say.

Some researchers have suggested that 30% of U.S. youth will be obese by 2030, but, the authors write, their data “suggest that the rapid increases in obesity prevalence seen in the 1980s and 1990s have not continued in this decade.”

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So have Americans finally begun to heed health messages about the risks of obesity? “I’m reluctant to speculate too much,” Flegal says.

Besides, she says, “there would be no real reason to expect the prevalence to go up and up and up. If you think it’s going to go up with time, it assumes there’s some obesity-increasing factor that’s going to increase with time.”

Perhaps Americans couldn’t get any heavier, theorizes Kelly Brownell, PhD, director of the Yale Rudd Center for Food Policy & Obesity.

“Maybe we just hit some natural plateau, where it simply can’t go any higher,” Brownell tells WebMD. “It’s somewhat of a victory, but the numbers are plateauing at a disastrous rate.”

Still, he says, “there have been some very significant changes in the way the country looks at the problem.” Instead of debating the merits of different diets, Brownell says, the press and the public are focusing on measures to prevent obesity, such as improving nutrition in schools and charging a soda tax. “The country is moving in the right direction,” he says.