New Obesity Index Proposed, But Further Work Needed

From Heartwire

Lisa Nainggolan

March 3, 2011 (Los Angeles, California) — US researchers have developed a new index of adiposity that they say is a more accurate measure of body fat than the traditionally used body-mass index (BMI); the latter is calculated by dividing weight by height [1].

Using measurements of hip circumference and height, the new body adiposity index (BAI) can be used to reflect percentage of body fat for adult men and women of differing ethnicities, without numerical correction or assessment of weight, say Dr Richard N Bergman (University of Southern California, Los Angeles) and colleagues in their paper published online March 3, 2011 in Obesity.

It remains to be seen if the BAI is a more useful predictor of health outcome than other indexes of body adiposity, including the BMI.

However, they note that further work will be needed to extend and confirm their findings--tested in Mexican Americans and African Americans--to whites and other ethnic groups and to assess the role of the new index in children. And "it remains to be seen if the BAI is a more useful predictor of health outcome, in both males and females, than other indexes of body adiposity, including the BMI itself."

Height and Hip Size Most Strongly Relate to Percentage Adiposity

"We were interested in determining whether we could find an index of body adiposity that at least in some ways may be better than the BMI, which has been around since the 1840s" and is not a very accurate measure of adiposity in individual patients, Bergman explained to heartwire .
BMI is particularly inaccurate in people with elevated lean body mass, such as athletes, and in children, and it cannot be generalized among different ethnic groups, he and his colleagues note.

Bergman et al are not the first to propose an alternative to BMI. Waist circumference is widely thought to be a better indicator of cardiovascular risk than BMI, although some studies have shown them to be equally predictive.
Other examples include the waist-to-hip ratio (WHR) and the waist-to-hip-to-height index, which have both been forwarded as potentially better measures of obesity than BMI. But critics have said that it is difficult and time-consuming to get very accurate measurements of waist and hip circumference and height and that BMI has remained popular because it is simple and fast.

We looked at which variables most strongly related to percent adiposity, and they were height and hip size.

In their study, Bergman and colleagues used a large database, BetaGene, which consisted of relatives of Mexican Americans with gestational diabetes, to determine whether there might be a better index. They chose the Mexican American population because of its prevalence in Los Angeles, observing, "Most of the world population is nonwhite."

"We looked at which variables most strongly related to percent adiposity, and they were height and hip size. Because these variables were uncorrelated, we proposed a new index, the BAI, based upon these measures alone," Bergman explains.

BAI Will Be Easy to Calculate

"We showed that the BAI, calculated as (hip circumference/height1.5)–18, was a good predictor of percent fat and worked for men and women," he continues. The BAI also yielded the percentage of fat itself, rather than just a correlate (or index) of it, which is what the BMI does, he notes. The BAI was validated against the "gold standard" of dual-energy X-ray absorption (DEXA).

"It will be very easy for a physician or a nurse practitioner to work out this index for individual patients, using a calculator, a computer program, or an iPhone app," Bergman says.

The researchers then went on to corroborate their findings in another population, the Triglyceride and Cardiovascular Risk in African Americans (TARA) study, and found that the behavior of the BAI was quite similar between the blacks in that population and the Hispanics in BetaGene.

"Thus, we believe that we have presented evidence of accuracy at least in two ethnic populations, and further work on the generalizability of BAI to other groups is under way," they state. It will also be important to see whether the index can reliably forecast percentage of adiposity in children and predict risk of cardiovascular disease, they note.