It is often suggested and is popular opinion that the obesity standards for Body Mass Index (BMI) overestimate obesity in populations. However, contrary to popular opinion, BMI may also underestimate obesity in sedentary individuals with low lean body mass. PURPOSE: The purpose of this study was to determine how frequently BMI over- or under-estimates obesityin a normal population. METHODS: Body composition data using hydrostatic weighing with estimated residual volume and BMI were collected on 415 males and 251 females. RESULTS: Descriptive Results-Males: age range 17 to 74, mean 28.9±12.9 years; body fat = 14.8±7.7%; BMI = 25.5±4.4 Kg/M2. Females: age range 18 to 68, mean 27.9±13.4 years; body fat = 23.1±10.1%; BMI =24.2±4.4 Kg/M2. Research Results-53 males (12.8%) and 34 females (13.5%) had BMI values <30 Kg/M2 (non-obese BMI values) but had % fat values of >20% and >30% (male and female obesity standards). Conversely, 22 males (5.3%) and 2 females (<1%) had BMI values > 30 Kg/M2 (obese BMI standard) but also had non-obese body fat of <20% males or <30% females. CONCLUSIONS: It is possible to have false positive obesity classification using BMI (high BMI, non-obese %fat). This was true in only 3.6% of our total population. However, we identified false negative obesity classification using BMI in 13.1% of our population who had non-obese BMI values but were obese using % fat standards. Thus, while popular belief is that BMI overestimates obesity we found the converse. In our large population, with average BMI and % body fat, we found a much higher percentage of individuals who were obese (excess fat) but had non-obese BMI values and would not have been classified as obese using BMI. Failing to identify obesity in sedentary individuals using BMI measurements could mask risk for cardiovascular and metabolic disease and delay preventative measures.

This document is currently not available here.