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We all know that measuring how fat you are involves more than just stepping on a scale

New Measurement of Body Fat Doesn't Include Weight

After all, a person who is 6 feet (or 183 cm) tall and weighs 220 pounds (100 kilos) is not as overweight as someone who is 4 feet (or 122 cm) tall and weighs 220 pounds (100 kilos). The taller you are, the more you should weigh. The question is how much more you should weigh.

Body mass index, better known as BMI, is a complex measurement comparing weight to the square of height. More confusingly for Americans, BMI involves metric measurements, dividing weight in kilograms by the square of height in meters (height x height). American measurements have to be converted to meters and kilograms before BMI can be computed.

Once the conversion is made, then the measurement supposedly accounts for height in measuring fatness. But BMI is hardly a perfect measurement.

For years, doctors, patients, and commentators have been complaining that the BMI is a poor measurement because it doesn't take into account that some people are more muscular than others, and that muscles are denser, and heavier, than fat. Athletes with lots of lean tissue get higher BMI scores. And different ethnic groups have different distributions of muscle and fat. That is why a research team at the University of Southern California, in Los Angeles, recently developed a Basal Adiposity Index, or BAI, that takes hip size into account.

How the Basal Adiposity Index Will Work

The University of Southern California researchers used a device called a dual-energy X-ray absorption scan or DEXA scanner to measure body fat in Mexican Americans and in Americans of Black heritage. Since Hispanics and African Americans tend to have very different body contours, any measurement that predicts body fat reliably in both groups would probably be useful for everyone.

The doctors found that of all the measurements that are relatively easy to take—without a DEXA scanner—the two that reliably predict the percentage of body fat are height and hip circumference. Unlike the BMI, it isn't necessary to step on the scales. What you weigh on the scales doesn't matter.

The University of Southern California research team is busy validating their scale for persons of European and Asian origins. Some fine tuning of the measurements is expected, but it is certain that no future version of the BAI will require use of scales to measure weight. Athletic individuals, of course, tend to have thinner hips, and the new scale will not penalize them for weighing more. People who have "jelly belly" fat, on the other hand, will have a higher BAI, even though "loose" fat packs fewer pounds at the scales.

The BAI has the potential to revolutionize weight measurements and dieting. No longer will people be slaves to losing weight. Soon doctors will have a way to measure whether or not dieting is actually making people healthy.

  • Bergman RN, Stefanovski D, Buchanan TA, Sumner AE, Reynolds JC, Sebring NG, Xiang AH, Watanabe RM. A Better Index of Body Adiposity. Obesity (Silver Spring). 2011 Mar 3. [Epub ahead of print]
  • Photo courtesy of Doc Searls by Flickr :