The body mass index (BMI) has become the most-used means of determining whether we are overweight or not, supposedly by measuring our body fat. Plug your height and weight into a BMI calculator and you’ll get a quick and dirty “definitive” answer. But where did BMI come from and how useful is it really?
BMI was invented in the 1800’s by a Belgian polymath named Adolphe Quetelet. It’s a mathematical calculation dividing a person’s weight by the square of his/her height. He was doing social research on what the “average man” looked like. His research had nothing to do with health. He was researching a lot of things, like a man’s arm strength or the age he marries.
The “pioneers” studying and pushing BMI for profit? Insurance companies. In the early 1900’s, motivated by their bottom line, life insurance companies started doing studies of BMI to show overweight people were more likely to have health problems and die earlier to show their policy holders.
In 1972 a professor and researcher named Ancel Keys published his paper “Indices of Relative Weight and Obesity.” He examined height-weight formulas and determined Quetelet’s was the best. Keys gave Quetelet’s formula the name “body mass index.”
BMI caught on. Instead of being used as studies of population health, doctors began using it as a quick way to measure body fat. But Keys had actually warned in his paper against using BMI for individuals diagnoses, since the equations ignores a lot of other variables, like exercise and ailments like high blood pressure. The Center for Disease Control (CDC) notes that BMI is only one factor to consider in determining weight problems:
BMI is used as a screening tool to identify possible weight problems for adults. However, BMI is not a diagnostic tool. For example, a person may have a high BMI. However, to determine if excess weight is a health risk, a healthcare provider would need to perform further assessments. These assessments might include skinfold thickness measurements, evaluations of diet, physical activity, family history, and other appropriate health screenings. Continue reading