Title of article:

An alternative to body mass index for standardizing body weight for stature.

Authors: Bagust A, Walley T.
Journal: QJM, Sep 2000;93(9):589-96

Abstract

Although body mass index (BMI) has been adopted by WHO as an international measure of obesity, it lacks a theoretical basis, and empirical evidence suggests it is not valid for all populations. We determined standard weight-for-height using a model calibrated by multivariate analysis of observational data on body dimensions and health status in the USA (NHANES III). A multiple linear regression model based on a simple mathematical formulation accurately described the observed weight variations in this normal adult population. A standardized reference model using just two measurements (upper arm length and sitting height), readily applied in both clinical and research settings using lookup tables, improved explanatory power substantially compared to the best BMI formulation (r(2) increased 16.3% for males, 21.1% for females). Physical dysfunction and self-reported poor health showed strong trends with excess body weight. These findings need confirmation from larger population samples.

Comments and Key points

Body Mass Index is based on height and weight. These authors offer an alternative called "Standard weight", based on sitting height and upper arm length.

Wow, something completely original. Their formulas are:

Male standard weight = -6.4704 - (3.1631*upper arm length) + (204.481*upper arm length²) - (4.6114*sitting height) + (74.5385*sitting height²).

Female standard weight = 4.7220 + (170.3938*upper arm length) - (848.4479*upper arm length²) + (1585.0379*upper arm length³) - (1.4922*sitting height) + 67.3340*sitting height²).

Units for upper arm length and sitting height, are expressed in meters.

Wow, these are complicated formulas, which probably scares people away from using them.

Anyway, the article has a few nice quotes:

" If the reference model is accepted as the more reliable, we conclude that the use of BMI tends to under-estimate the prevalence of overweight and obesity amongst the tallest men and women, and over-estimate it amongst the shortest". and also " according to BMI, female prevalence of obesity is strongly associated with height, whereas male prevalence is not".

" The 'standard weight'... does not define the 'ideal' or target weight unequivocally". ( which is their back-handed way of suggesting that their formulas could be used to define ideal weight.)

" The definition of obesity as BMI > 30 must be reconsidered if the new standard weight is adopted".

Overall, I didn't seem any specific advantage of switching from BMI to standard weight.

 

Review & comments by Steven B. Halls, MD, Changed/edited: 23-June, 2008, Copyright.
Back to Bibliography of BMI articles.