Gas station without pumps

2011 March 9

BAI: A Better Index of Body Adiposity

Filed under: Uncategorized — gasstationwithoutpumps @ 09:09
Tags: , ,

In the journal Obesity, there is an article, A Better Index of Body Adiposity, suggesting a new way to estimate how fat people are from simple measurements.  The authors hope to replace the body mass index with an equally simple index that does not need so many corrections for race and sex.

The new measure is indeed simple $\mbox{BAI} = p/h^{1.5} - 18$, where $p$ is the hip circumference in cm and $h$ is the height in meters.  The 18 is there to make the index be approximately the %fat for the individual, which was directly measured in the calibration sample of 1700 people using dual-energy X-ray absorptiometry (DXA).

I tried applying this measure to myself (104 cm hips, 1.8m tall), and got and estimate of 25% body fat. Hips are measured “at the level of the maximum extension of the buttocks posteriorly in a horizontal plane.”  Based on the calibration sample, this puts me in the range where BAI does a good job of estimating %fat.  The BAI measure tends to overestimate %fat at both the low end and the high end of the measurements, but for most of the calibration sample it was within about ±5.

My BMI is about 25.1–25.8. Using the formula
Adult body fat % = (1.20 x BMI) + (0.23 x Age) – (10.8 x gender) – 5.4
from Wikipedia’s Body fat percentage, I get an estimate of 26.8–27.6% body fat.  I think I like the BAI measure better, though I have no idea which is more accurate.  Both measures put me at the low end of the overweight range, which matches my self  image.

Of course, there have not been any studies yet to show whether BAI has a better diagnostic value than BMI, but it doesn’t seem to have different scales for males and females, the way that BMI does, so it is likely to be more useful.

1. In the formula for Adult body fat %, does the gender variable equal 1 for female and 0 for male, the reverse, or something else?

Comment by V.R. — 2011 March 10 @ 09:57

• Sorry, I copied only a piece of the Wikipedia page. The gender variable is 1 for male, 0 for female. (I would have given it a more mnemonic name, like “maleness”.)

Comment by gasstationwithoutpumps — 2011 March 10 @ 11:26

2. Update: I bought a scale and have a better estimate of my weight. My BMI is about 24.0, which makes an estimate of 25.5% fat, very close to the BAI estimate. Both put me at the high end of the normal range: just below “overweight”.

Comment by gasstationwithoutpumps — 2011 June 29 @ 09:30

3. […] Body Adiposity Index now estimates my body  fat at 23.4%, while the estimate from BMI is 24.8%.  According to some […]

Pingback by Twelfth weight progress report (one year) | Gas station without pumps — 2015 December 31 @ 15:58

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