WASHINGTON, DC -- After a quarter century of increases, obesity prevalence has not measurably increased in the past few years but levels are still high –- at 34 percent of U.S. adults aged 20 and over, according to a study released this week by the Centers for Disease Control and Prevention (CDC).

The report, "Obesity Among Adults in the United States—No Change Since 2003-2004," is the latest analysis based on the National Health and Nutrition Examination Surveys, conducted by CDC’s National Center for Health Statistics.

Obesity rates have increased during the past 25 years. Among men, an increase in obesity prevalence occurred between 1999 and 2006. However, no significant change in obesity prevalence occurred between 2003-2004 and 2005-2006 for either men or women.

"Since 1999, there appears to have been a leveling off in obesity among women, but the trend is less clear among men. We do know however that the gap between men and women has narrowed in recent years, with men catching up to the higher rates among women," says Cynthia Ogden, a CDC researcher and lead author of the study.

Obesity is defined as a body mass index of 30 or higher.

The study found that more than one-third of U.S. adults – more than 72 million people -- were obese in 2005-2006. This includes 33.3 percent of men and 35.3 percent of women. The figures show no statistically significant change from 2003-2004, when 31.1 percent of men were obese and 33.2 percent of women were obese.

Adults aged 40-59 had the highest obesity prevalence compared with other age groups. Approximately 40 percent of men in this age group were obese, compared with 28 percent of men aged 20-39, and 32 percent of men aged 60 and older. Among women, 41 percent of those aged 40-59 were obese compared with 30.5 percent of women aged 20-39. Women aged 65 and older had obesity prevalence rates comparable with women in the 20 to 39 age group.