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Americans may be fatter than known, using BMI only

Kathleen Blanchard's picture
BMI not useful for measuring obesity, finds study

Body mass index (BMI), which is commonly used to diagnose obesity may be responsible for underestimation of America’s obesity epidemic, finds a new study. Using a different measurement than BMI show Americans are fatter than previous estimates show.

Researchers found many Americans who have been classified as overweight are actually obese, based on Dual Energy X-ray Absorptiometry (DXA) scans that measure body fat, muscle mass, and bone density simultaneously. The finding, published in the journal PLoS ONE, found that 39% of people classified as overweight are obese according to DXA measurements.

Direct measurement of body fat reveals obesity

Eric Braverman, M.D., one of the authors of the study explained in a press release that measuring BMI really is an inaccurate way to measure body fat distribution. The study is published in the journal "PLoS One".

BMI is easy and low cost, but Braverman and Nirav Shah, M.D., M.P.H. and study author, say it’s simply outdated.

Another way to measure body fat they say is by measuring leptin levels, combined with BMI when DXA scans aren’t available. The BMI chart could be altered to include leptin to gauge obesity.

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Fat and especially where it’s distributed is linked to metabolic health. Waist in the abdomen is known to be more harmful, raising the risk of disease, compared fat in the hips. Simply measuring BMI – weight to height measurements - doesn’t tell the whole story.

"These estimates are fundamental to U.S. policy addressing the epidemic of obesity and are central to designing interventions aimed at curbing its growth," the authors say, "yet the [current policies] may be flawed because they are based on the BMI."

This isn’t the first study to question the value of BMI for determining overweight and obesity.

A study presented at the Endocrine Society’s 91st annual meeting in Washington DC in June 2009 also suggested separating reference values for Whites, African Americans, and Mexican Americans. Researchers also suggested separate reference values for children and adolescents.

The new finding suggests it may be time to get rid of BMI as a tool for measuring who is overweight or obese. The authors explain body mass index doesn’t account for individuals with high leptin levels, which correlates with body fat, women of advancing age and normal weight obese people; suggesting America’s obesity epidemic may be worse than we know.

PLoS One
"Measuring Adiposity in Patients: The Utility of Body Mass Index (BMI), Percent Body Fat, and Leptin"
Nirav R. Shah, Eric R. Braverman
April, 2012

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