Perspective on the Body Mass Index (BMI) and Variability of Human Weight and Height

The body mass index (BMI) is a medical risk factor that has been in use since 1972 to identify degrees of weightiness, in particular obesity and severe underweight. Over the past few years there has been much strident criticism of the BMI in traditional news media, health-related internet sites, and some medical journals over whether the index adequately identifies obesity of individuals in diverse demographics. As the research scientist (nuclear and medical physicist) who recently derived the exact statistical distribution functions of human weight, height, and BMI, I have found that much of this criticism is based on misunderstanding and misuse of the statistical nature of the BMI. In this Perspective, I attempt to make clear (1) what the BMI is, (2) why it was defined as it was, (3) how human height, weight, and BMI vary in a population, (4) the effective way to employ the BMI in clinical settings, and (5) what criteria to bear in mind if the BMI is to be replaced by some other medical index.