MINNEAPOLIS, April 14, 2008—Mayo Clinic cardiologist Francisco Lopez-Jimenez, M.D., has a new label for physicians to use: normal weight obesity.

It sounds like an oxymoron, but it describes something very real: people whose weight may be normal, but who still have too much body fat.

They may be people who are out of shape, and have less muscle mass.

"The definition of obesity is having excess fat," says Lopez-Jimenez, senior author of a study on normal weight obesity, and a member of the MMA.  

The study was presented recently at the American College of Cardiology's annual science session in Chicago.

"For years we've been using BMI to diagnose obesity," Lopez-Jiminez told the Los Angeles Times. "But the first question we had was 'Is it possible to be normal weight but have excess fat?' "

His research team looked at data from the National Health and Nutrition Examination Survey and found that among 2,127 men and women of normal weight and BMIs between 18.5 and 24.9, almost half had excess fat — 20 percent of total body composition for men and 30 percent for women.

Compared to people without excess fat, these cases of normal weight obesity were 2.5 times more likely to suffer from metabolic syndrome.

Bottom line: weight and BMI are not perfect indicators. It's body fat that compromises cardiovascular health, not the number on the scale.