A report published yesterday in the Public Library of Science's PLoS One journal (clever) suggests that the body mass index (BMI), the formula commonly used to determine whether an individual is of a healthy weight, may be underestimating obesity in almost 40 percent of cases.
The study pitted notoriously fallible BMI calculations against expensive-sounding dual-energy x-ray absorptiometry (DXA) scans.
The main difference between the two methods is that the BMI estimates body fat based on a person's height-to-weight ratio, while the DXA test provides a direct measurement of the amount of fat (and muscle mass and bone density) in a body.
In other words, the DXA scan proves what everybody already knows when you say you're overweight because you're big boned and have a lot of muscle: you lyin'.
Almost half of the study's female participants whose BMI numbers identified them as "overweight" were found actually to be obese, when measured by the more accurate DXA scan. Study author Dr. Eric Braverman explains that the BMI is likely most misleading for older women, since they lose muscle and bone and replace them with fat faster than men.
One quarter of male subjects whose BMI numbers classified them as merely overweight were found to be obese by the DXA scan.
While the Centers for Disease Control use the BMI to estimate that about one third of Americans are obese, Dr. Braverman suggests the actual figure may be closer to 60 percent.
He also threw out this parting snap:
"Some people call it the ‘baloney mass index.'"
Taking shots at both the BMI and a popular lunch meat. A brave man indeed.