BODY-MASS INDEX - A MEASURE OF FATNESS OR LEANNESS

The relationship between body fat and stature-adjusted weight indices was explored. Assuming the term height(2) is a valid indicator of a su bject's lean body mass, height(2)/weight was shown to be an accurate m easure of percentage lean body mass and, as such, a better predictor o f percentage body fat than the traditional body mass index (BMI; weigh t/height(2)). The name, lean body mass index (LBMI), is proposed for t he index height(2)/weight. These assumptions were confirmed empiricall y using the results from the Allied Dunbar National Fitness Survey (AD NFS). Using simple allometric modelling, the term height(p) explained 74% of the variance in lean body mass compared with less than 40% in b ody weight. For the majority of ADNFS subjects the fitted exponent fro m both analyses was approximately p = 2, the only exception being the female subjects aged 55 years and over, where the exponent was found t o be significantly less than 2. Using estimates of percentage body fat as the dependent variable, regression analysis was able to confirm th at LBMI was empirically, as web as theoretically, superior to the trad itional BMI. Finally, when the distributional properties of the two in dices were compared, BMI was positively skewed and hence deviated cons iderably from a normal distribution. In contrast, LBMI was found to be both symmetric and normally distributed. When height and weight are r ecorded in centimetres and kilograms respectively, the suggested worki ng normal range for LBMI is 300-500 with the median at 400.