By Caitlin Dow, Student Blogger

Body Mass Index. BMI, for short. Those three words tend to conjure up some intense feelings in scientists and the general public, alike. In 1832, a Belgian statistician named Adolphe Quetelet created his namesake index, the Quetelet Index, to describe the normal variation seen in weight relative to height across populations. That index got its new name “Body Mass Index” in 1972 from Ancel Keys (1) and was  by the World Health Organization as a clinical tool to be used easily and effectively to determine levels of obesity.


As Cyndi Thomson, PhD, RD, a professor in the College of Public Health at the University of Arizona points out, “BMI was meant for population evaluation and we keep applying it to individuals.” BMI is useful when we study populations. It predicts risk for development of a number of chronic diseases (2). However, applying BMI to individuals, which is likely not what Quetelet had in mind when he created it, creates a number of issues. While BMI correlates well with fat mass on a population (but not necessarily on an individual level), it certainly does not consider distribution of fat. This is important because plenty of data indicate that abdominal fat predisposes people to a number of health risks more so than fat distributed evenly throughout the body (2). Furthermore, associations between BMI and various outcomes like risk for disease or mortality are assumed to be linear. That is, as BMI increases, risk for disease also increases. However, some cross-sectional, epidemiological studies have shown a “U-shaped” relation between BMI and mortality (3,4), meaning that people with very low or very high BMIs are at elevated risk of dying within a given period of time than those in the middle (generally overweight) range. The increased mortality risk with normal BMIs later in life is actually probably due to smoking or weight loss due to disease (like cancer), but this hasn’t stopped the media from concluding that “being overweight is good for you!” Due to these shortcomings of BMI, it is high time to consider/develop some type of index that (a) has a linear relation with mortality for ease of interpretation; (b) considers fat mass and/or distribution; and (c) can be used easily in both research and clinical settings.