BMI, Body Build, Body Fatness, and Health Risks

Abstract

The body mass index (BMI) is often criticized because it is an inaccurate index of body fat. However, implicit in this criticism is that a better indicator of body fat would be acceptable as a means of separating unhealthy fat people from healthy thin people. In fact, measures of body fat percentage are readily available and are not superior to the BMI as indicators of health risks. The BMI was developed as an index of overall body size by removing the influence of body height on body weight. Using height and weight data on 1,034 major league baseball players, the usefulness of the BMI is illustrated in two scatter plots. Height and weight are clearly related, whereas height and BMI are completed unrelated. Epidemiological studies are reviewed that have determined BMI and percent body fat in relation to death rates and risk factors. In no instance is percent body fat superior to BMI in predicting risk, and BMI is actually more closely related to risk factors than is body fatness. Thus, excess muscle mass or large body size may be a significant predictor of disease that is captured by BMI. Importantly, although weight loss can reduce body fat, it cannot remake body size or muscularity.