Obesity is defined differently for adults and children. Adults with a body mass index (BMI) of 30 or more are considered obese. BMI is a calculation based on weight and height. Children are deemed obese if their BMIs are greater than or equal to the 95th percentile on growth charts. Obesity raises a person’s risk of developing diabetes, heart disease, sleep apnea, stroke, and some cancers, among other health issues, according to many experts.

Adult waistlines haven’t expanded since 2003, according to the study, which analyzed data from the CDC’s National Health and Nutrition Examination Survey from 2009-2010 and compared them to data from earlier periods. More specifically, women haven’t gotten any more obese than they were in 1999, while the rate for men hasn’t changed significantly since 2003.

Overall, children also don’t appear to have gotten heavier. The U.S. childhood obesity rate has leveled off in recent years after more than tripling since the early 1980s.

“It’s really pretty flat,” Katherine Flegal, a CDC epidemiologist and an author of both studies, says of the obesity rates in recent years. And, “this is happening all over the world.”

In a studythat she and several others published last year in the International Journal of Pediatric Obesity they reported that the prevalence of childhood obesity has slowed, or leveled off, in nine countries, including China, Australia, and England as well as the U.S.

The reasons for the leveling off — like the sharp increase that preceded it — aren’t precisely clear, the papers say. Flegal and her colleagues cite the usual array of presumed factors: an expansion of the food supply, energy imbalance, the possible effect of environmental endocrine disruptors. But they say more research is needed into the factors causing the sharp rise, as well as the plateau now.

The data however is not all roses. The obesity epidemic is still there - Americans aren’t getting any thinner, nor are populations in other countries. More than one in three U.S. adults — 35.7% — were obese in 2009-2010. That’s 78 million people. And about one in six children — 16.9% — were obese in the same years. That’s 12.5 million kids.

While current data opposes the epidemic rates predicted by many expects, it is not out of the question that obesity rates could start rising again. High rates concern doctors and public health experts because it costs millions of dollars to treat obesity-related diseases such as heart disease and Type 2 diabetes. High obesity rates have also deepened health disparities. Obesity rates for black and Mexican-American women rose between 1999 and 2010, for example. Hispanic and black children have higher obesity rates than white children.

Here are some of the key details from the CDC's latest reports and obesity statistics:

• The CDC's findings were part of two separate reports, one focusing on the obesity rate in U.S. adults and the other focusing on the obesity rates among American children. Both have been published in the Journal of the American Medical Association.
• Obesity in adults concluded that rates plateaued between 2009-2010 at approximately 35.5 percent for men and 35.8 percent for women.
• While the overall rate of obesity among women has remained essentially the same over the last decade, specific groups have seen increases, particularly Mexican American and non-Hispanic black women.
• The rate of obesity among men remained essentially the same across all groups.
• This leveling off follows more than two decades of marked increases in the rate of obesity in U.S. adults. From 1976 to 1999, the rate had increased by approximately 16 percent.
• Obesity in children had leveled off between 2009-2010 to remain at approximately 16.9 percent.
• Obesity levels did increase significantly among male children between 1999-2010, but not among female children. This is the first time that the obesity rate among male children was found to be higher than among female children.
• The CDC reports are based on health surveys that are conducted across the United States every two years. The most recent report, from 2009-2010, included some 6,000 adults and 4,000 children. Children are charted from infancy all the way up to age 19.
• In addition to the number of adults and children whose BMI indicated that they are obese, another 33 percent of adults and 15 percent of children had a BMI ranking that indicated that they are overweight.