The number of U.S. adults and children who are obese has remained relatively constant over recent years, according to a pair of studies published in the Journal of the American Medical Association.

Two reports, one about adult obesity, and the other focused on obesity in children, found that in 2009 and 2010, about one in three adults and one in six children and teens were obese. The ratios showed no change from the 2007-2008 figures and, aside from a few specific demographics, demonstrated only a slight increase in the prevalence of obesity from turn of the century numbers.

The researchers analyzed data from the National Health and Nutrition Examination Survey, in which participants were weighed and measured between 2009-2010. From that data, researchers calculated each individual’s weight-to-height ratio, or body mass index.

As the number of individuals who were obese increased considerably throughout the 1980s and 1990s, many expected that the trends would continue into the next century, causing rates of type 2 diabetes and heart disease to spike. The newest data, however, shows virtually no change in the rates of obesity since the last survey in 2007.

The population prevalence of obesity in the adult population showed little change in the period 1960 through 1980, followed by an increase of almost 8 percent between the 1976-1980 survey and the 1988-1994 survey.

A similarly large jump in obesity rates occurred between the 1988-1994 survey and the 1999-2000 survey. Over the period 1999-2008, however, there was a much smaller change in the prevalence of obesity in men, and no statistically significant changes in the prevalence of obesity in adult women.

Though the study on childhood obesity found that there was “no difference in obesity prevalence among males or females between 2007-2008 and 2009-2010,” researchers noted that certain demographics showed significant differences in obesity rates. The prevalence of obesity in male children aged 2 through 19 years (18.6 percent) was much higher than among female children in the same age bracket (13 percent).

Furthermore, obesity rates in certain ethnicities were much higher. In 2009-2010, 21 percent of Hispanic children and adolescents and nearly 25 percent of non-Hispanic black children and adolescents were obese compared to 14 percent of non-Hispanic white children and adolescents. The plateauing of obesity rates suggests that public health programs promoting healthier lifestyles are making an impact. But that doesn’t negate the fact that one third of the U.S. population is still obese.

“I believe we’re not yet at the place with obesity where tobacco was when cigarette use started to drop,” says Dr. William Dietz, director of the division of nutrition, physical activity and obesity at the CDC. “Nutrition programs and physical activity efforts have only just begun to kick in, and haven’t had much time to operate. It takes time before the effects of policy change begin to show benefit in terms of behavior changes.”