COLORADO SPRINGS — As if the obesity epidemic wasn't serious enough already, it turns out more than half of individuals with a normal body mass index have a condition called normal-weight obesity.
Normal-weight obesity—defined by a high percentage of body fat in the presence of a BMI in the normal range of 18.5–24.9 kg/m
“By screening for high body fat in subjects with a normal BMI, we were able to identify a subset of patients at higher risk for cardiovascular disease. This is very important because self-awareness is always the first step for behavioral modification. Most of the cardiometabolic dysregulation seen in these patients is potentially reversible through diet, physical activity, and possibly pharmacotherapy,” said Dr. Romero-Corral of the Mayo Clinic, Rochester, Minn.
He presented a cross-sectional study involving 2,127 adults with normal BMI and a mean age of 41 years who participated in the Third National Health and Nutrition Examination Survey (NHANES-3). All of them underwent body fat composition measurement by bioelectrical impedance, a full cardiovascular and metabolic risk factor assessment, and fasting morning blood tests.
Fifty-five percent of subjects had normal-weight obesity as defined by greater than 20% body fat in men and greater than 30% in women. This would translate into 45 million affected Americans, extrapolating from the NHANES-3 findings using 2006 census data. Although there is no official consensus on criteria for obesity based on body fat, “I think most physicians will agree that 20% and 30% are high,” Dr. Romero-Corral said in an interview.
Hispanics had the highest prevalence of normal-weight obesity, at 71%, followed by blacks at 61% and whites at 53%.
Normal-weight obesity is not a benign phenomenon, Dr. Romero-Corral emphasized. After adjusting for age and race, normal-weight obese men had a 68% greater likelihood of meeting ATP-III criteria for metabolic syndrome, compared with men who had normal BMIs and normal body fat. And normal-weight obese women had nearly a threefold increased prevalence of metabolic syndrome compared with women who had normal BMIs and normal body fat.
All of the numerous cardiometabolic parameters measured in this study trended unfavorably in the normal-weight obesity group. Many of these adverse effects achieved statistical significance (see box).
Women with normal-weight obesity were four times more likely to have known cardiovascular disease than were controls.
This study underscores the BMI's drawbacks as a tool for diagnosing obesity. BMI doesn't distinguish between body fat and lean mass, which have very different biologic effects. “We know lean mass is protective because it's related to greater physical activity and a better metabolic profile,” the physician noted.
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