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Is the new BAI better than the old BMI?


An increasing dissatisfaction with the use of Body Mass Index (BMI) for measuring obesity has led scientists to develop a new way to measure obesity without having people step on the scale.

The new measure, called the Body Adiposity Index, or BAI, relies on height and hip measurements whereas BMI relies on a ratio of height and weight.

Richard Bergman of the University of Southern California, Los Angeles, and colleagues have published their findings on the new BAI in the journal Obesity.

Obesity is a growing problem in the United States and throughout the world. It is a risk factor for many chronic diseases. BMI is used in many schools to assess at risk children for obesity.

BMI was invented by Lambert Adolphe Quetelet more than 200 years ago. His Body Mass Index (also called the 'Quetelet Index') which remains the current “simple” measurement for obesity to this day.

BMI is not without its flaws. Many believe it is only valid for people over the age of 20. It often puts professional athletes in an obese range, as it only measures total weight in relation to height and does not take into account body fat or body fat percentage.

Women and men with the same BMI might have very different levels of extra flab. BMI numbers cannot be generalized across different ethnic groups or used with athletes.

It is calculated by dividing weight in kilograms by height in meters squared. A person who is 5 feet 5 inches tall is classified as overweight at 150 pounds (68 kg) and obese at 180 pounds (82 kg).

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For most average Caucasian BMI is a convenient and reasonably accurate measurement of whether we are underweight (below 18.5); normal weight (18.5-24.9); overweight (25 – 29.9); or obese (30.0 or above).

So will the new Body Adiposity Index, or BAI, be better?

Perhaps, as the BAI uses a complex ratio of hip circumference to height. Hip circumference (R = 0.602) and height (R = −0.524) are strongly correlated with percentage of body fat.

Body adiposity index (BAI = ((hip circumference)/((height)1.5)–18)).

Bergman and colleagues developed the BAI index using data from a Mexican-American population study. Percentage of body fat, as measured by the dual-energy X-ray absorptiometry (DXA), was used as a “gold standard” for validation of the scale’s accuracy.

The BAI measure was validated in the “Triglyceride and Cardiovascular Risk in African-Americans (TARA)” study of African Americans. Correlation between DXA-derived percentage of adiposity and the BAI was R = 0.85 for TARA with a concordance of C_b = 0.95.

BAI can be measured without weighing, which may render it useful in settings where measuring accurate body weight is problematic. It can be calculated by doctors or nurses with a computer or calculator.

The researchers say BAI still needs to be tested among whites and other ethnic groups.

A Better Index of Body Adiposity; Bergman RN, Stefanovski D, Buchanan TA, Sumner AE, Reynolds JC, Sebring NG, Xiang AH, Watanabe RM; Obesity (2011) doi:10.1038/oby.2011.38

Famous Belgians: Lambert Adolphe Quetelet (1796-1874)