When it comes to the average person, body mass index doesn't lie

From News Center (4/29/2005)

Despite heavily publicized media reports that body mass index (BMI) labels pro football and basketball players as obese, the system does work for the average person, says new research by Ball State University.

An analysis of 3,775 men and women who completed testing in 2003 for Ball State's Adult Physical Fitness Program found that just three percent were misclassified, said Leonard Kaminsky, a physical education professor. He conducted the study with Mitch Whaley, chair of Ball State's School of Physical Education, as part of an investigation by Ball State's Human Performance Laboratory.

A popular method used to gauge whether or not a person is overweight, BMI is calculated by dividing a person's weight by his or her height. Body fat criteria for obesity is 20 percent for men and 27 percent for women.

However, when it is applied to professional athletes, many are listed as obese because of having a high percentage of muscle, Kaminsky said.

"It is clearly accepted that in some athletic populations and in those who perform high levels of resistance-type exercise or activities the BMI can result in a substantial number of obesity misclassifications," he said. "BMI is not meant for professional athletes because the index does not distinguish between fat and muscle. A 230-pound basketball player may be listed as obese but may have less than 10 percent body fat and be in incredible shape."

The study found that 687 participants were classified as obese, and only 20 would have been misclassified as obese by BMI according to body fat criteria.

"The present data demonstrates that the BMI can accurately detect obesity in the general adult population," Kaminsky said. "This suggests that clinicians can consider the index as the primary obesity assessment measure for adults.

"National statistics show that obesity rates have climbed to 27 percent of the population in 1999 from 15 percent in 1976," he said. "BMI may be the best way to give a good picture of people's health and help them address their weight problems."