US obesity measures ‘flawed’
MedWire News: The prevalence of obesity in the USA may be higher than previously thought, suggests a study published in PLoS ONE.
The researchers found that body mass index (BMI), the most common measure of adiposity, significantly underestimates obesity when compared with dual-energy X-ray absorptiometry (DXA), a direct simultaneous measure of body fat, muscle mass, and bone density.
Indeed, 39% of study participants were classified as non-obese by BMI but were found to be obese by DXA.
The findings come from a cross-sectional study of 1393 adult patients (mean age 51.4 years) who had BMI and DXA measures taken between 1998 and 2009. A BMI of 30 kg/m2 or more was used to classify patients as obese, while men with a body fat percentage of 25% or more and women with a body fat percentage of 30% or more were classified as obese by DXA.
The study found that the mean BMI of the study population was 27.3 kg/m2 and the mean percent body fat was 31.3%.
DXA classified 64% of participants as obese, while BMI indicated that just 26% were obese.
Misclassification was seen more often in women than men; 48% of women were classified as non-obese by BMI, but were found to be obese by percent body fat, compared with 25% of men. In women, there was also a positive correlation between advancing age and misclassification.
The researchers attempted to identify new cut-points for BMI that would better categorize patients as obese. Using percent body fat as the gold standard they say that more appropriate cut-points would be 24 kg/m2 in women and 28 kg/m2 in men.
They found that using these cut-points, instead of a BMI of 30 kg/m2, would increase diagnostic sensitivity from 35% to 79% in women and from 51% to 72% in men, with only a 13% and 12% loss of specificity, respectively.
Nirav Shah (New York School of Medicine, USA) and Eric Braverman (Weill-Cornell Medical College, New York, USA) say that their findings suggest that obesity, body fat, and increased adiposity are more prevalent than the American public and physicians are aware of. "This is contributing greatly to multiple co-morbidities such as hyperlipidemia, coronary artery disease, hypertension, and diabetes," they say.
However, the authors note that the current underestimation of adiposity in large scale studies, and subsequent use of such studies for public health policy-making, can readily be corrected. "Improving this globally used metric [BMI] will have broad population health implications," they conclude.
MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2012
By Nikki Withers