The History Of Body Mass Index

The body mass index, which is known as BMI, measures body fat and assesses your risk of getting obesity-related diseases. The index is a simple equation--weight in kilograms divided by height in meters squared. It was created under a different name in 1832 and wasn't used for assessing disease risks until the 1970s.

Quetelet Index

Belgian mathematician Adolphe Quetelet was trying to find the correlation between a man's height and weight as part of his project to learn the average measurements of men, according to "Beyond BMI," an article in the July 20, 2009, issue of "Slate" magazine. Quetelet measured and weighed several hundred Belgians. He learned that there was no direct correlation between height and weight, but there was a correlation between height squared and weight.

Landmark Study

The Quetelet Index became part of a landmark study in 1972, according to "Beyond BMI." Medical researchers studying the link between obesity and longevity were dissatisfied with the insurance companies' weight-for-height tables because they used subjective assessments of body frame (small, medium, large). The researchers wanted one standard equation. University of Minnesota professor Ancel Keys measured the height, weight and body fat of more than 7,400 men and compared the results to several height-weight equations.

Researchers Accept BMI

Keys renamed the Quetelet Index the body mass index after he learned that the weight divided by height squared equation was the most accurate measurement of body fat. Medical researchers then went back into their records and learned that there was a correlation between the BMI and obesity-related diseases, "Beyond BMI" reported. The researchers preferred the BMI to Keys' more direct ways of measuring body fat because learning BMIs was easier and less expensive.

Doctors Accept BMI

Doctors began making weight-loss recommendations to patients based on the BMI instead of weight-for-height tables after Keys' research became well-known, and the National Institutes of Health made BMI its obesity definition in 1985, "Beyond BMI" reported. The agency categorized BMIs as underweight, normal and overweight. You were overweight if your BMI--27.8 for men and 27.3 for women--was higher than 85 percent of people who were the same height.

BMI Changed

The National Institutes of Health changed the BMI classifications in 1998. The agency decided the same standards should apply to men and women although "at the same BMI, women tend to have more body fat than men," the Centers for Disease Control and Prevention reported. The BMI's overweight standard was changed to 25.0 to 29.9, the normal standard became 18.5 to 24.9. A fourth category, obese, was added for people with BMIs 30 and higher.

Statistics

Americans' BMIs increased significantly from the early 1960s through 2002, according to the National Health Examination Survey and the National Health and Nutrition Examination Surveys. Men's mean BMIs increased from just over 25 in the early 1960s to 26.7 from 1988 through 1994, and to 27.8 from 1999 through 2002. Women's mean BMIs increased from just under 25 in the early 1960s to 26.5 from 1988 through 1994, and to 28.1 from 1999 through 2002.