July 14, 2010 -- Men who are obese at age 20 are twice as likely to die young, according to new research presented at the International Congress on Obesity in Stockholm, Sweden.

As it stands, more than two-thirds of U.S. adults aged 20 and older are overweight or obese, according to the National Institutes of Health in Bethesda, MD.

"Entering adult life as obese leads to a life-long doubling of the risk of dying prematurely," study researcher Esther Zimmermann, PhD, of the Institute of Preventive Medicine in Copenhagen University Hospital in Denmark, tells WebMD in an email. "The best advice is to avoid beginning adult life as obese [because] if you enter adult life as obese, the majority will remain obese as adults."

Zimmerman and colleagues tracked about 5,500 Swedish men from age 20 to age 80 and found that the 1,930 men who were obese when they were 20 were twice as likely to die at any given age than were their counterparts who were not obese at age 20. Starting at age 55, men who were obese at 20 died an average of eight years earlier than their counterparts who were not obese at age 20.

What's more, their chance of dying early increased by 10% for each body mass index (BMI) unit above 25. BMI takes height and weight into account to measure body fat. If your BMI is greater than 25, you are considered overweight. If it is over 30, you are considered obese.

Study participants completed follow-up surveys at age 35 and 46. More than 70% of men who were obese at age 20 remained so during these follow-up exams. By contrast, just 4% of men who were not obese at age 20 went on to become obese, the study showed. Researchers adjusted for other factors known to affect mortality such as smoking status.

"Entering adult life as obese had a life-long effect on mortality," she says. The next step is to study why those individuals who were obese at age 20 died earlier, she says.