WASHINGTON (Reuters) - The number of obese American adults outweighs the number of those who are merely overweight, according to the latest statistics from the federal government.

Subway riders walk through the turnstiles while leaving the U.S. Open in New York September 4, 2007. REUTERS/Lucas Jackson

Numbers posted by the National Center for Health Statistics show that more than 34 percent of Americans are obese, compared to 32.7 percent who are overweight. It said just under 6 percent are “extremely” obese.

“More than one-third of adults, or over 72 million people, were obese in 2005-2006, the NCHS said in its report.

The numbers are based on a survey of 4,356 adults over the age of 20 who take part in a regular government survey of health, said the NCHS, which is part of the Centers for Disease Control and Prevention.

The figures come from the 2005-2006 survey and are the most current available.

“During the physical examination, conducted in mobile examination centers, height and weight were measured as part of a more comprehensive set of body measurements,” the NCHS report said.

“Although the prevalence of obesity has more than doubled since 1980, the prevalence of overweight has remained stable over the same time period,” it said.

Obesity and overweight are calculated using a formula called body mass index. BMI is equal to weight in kilograms divided by height in meters squared. Someone with a BMI of 25 to 29 is classified as overweight, 30 to 40 counts as obese and people with BMIs of 40 or more are morbidly obese.

A person 5 feet 5 inches tall becomes overweight at 150 pounds (68 kg) and obese at 180 pounds (82 kg). The U.S. National Institutes of Health has an online BMI calculator at www.nhlbisupport.com/bmi/.

In the 1988-1994 surveys, 33 percent of Americans were overweight, 22.9 percent were obese and 2.9 percent were morbidly obese. The numbers have edged up steadily since.

Being overweight or obese raises the risk of heart disease, diabetes, some cancers, arthritis and other conditions.

In May, the CDC reported that 32 percent of U.S. children fit the definition of being overweight, 16 percent were obese and 11 percent were extremely obese.

Childhood and adult obesity has emerged as a growing problem not only in the United States but also in many countries around the world.