We use it every time we visit a doctor. Insurance companies use it to determine premiums. But where did the Body Mass Index (BMI) come from? Surprisingly, it wasn't invented by a doctor, but by a mathematician obsessed with finding the "Average Man."
1832: The Quetelet Index
In the early 19th century, Belgian statistician Adolphe Quetelet was fascinated by human growth trends. After analyzing data from thousands of people, he discovered a consistent mathematical relationship: except during growth spurts after birth and puberty, weight increases as the square of height.
He termed this the Quetelet Index (`Weight / Height²`). Crucially, he never intended it to be a measure of individual fatness or health—it was purely a statistical tool for population studies.
1972: Enter Ancel Keys
"The body mass index... appears to be preferable to other indices of relative weight." — Ancel Keys
For nearly a century, the Quetelet Index gathered dust. Then, in July 1972, American physiologist Ancel Keys published a landmark study in the Journal of Chronic Diseases. He compared various weight-height ratios and found Quetelet's formula was the best proxy for body fat percentage.
Keys renamed it the Body Mass Index (BMI). However, like Quetelet, Keys explicitly warned against using BMI for individual diagnosis.
1985-1998: The Shift in Standards
In 1985, the U.S. National Institutes of Health (NIH) adopted BMI as the standard for defining obesity. Originally, the "overweight" threshold was 27.8 for men and 27.3 for women.
However, in 1998, the NIH (followed by the WHO) lowered the threshold to match global standards:
- Overweight: Lowered from 27.8 to 25.0
- Obese: Defined as 30.0+
Overnight, millions of Americans who were previously considered "healthy" woke up classified as "overweight" without gaining a single pound. This shift was controversial but was aimed at aligning global health data.
Where Do You Stand Today?
Use the modern WHO standards to check your current BMI category instantly.
Check My BMIModern Controversies
Today, BMI is under fire. Critics argue it is flawed because:
- It cannot distinguish between muscle and fat (The "Rock" would be classified as obese).
- It ignores waist circumference, which is a better predictor of heart disease.
- It was based primarily on White European men, making it less accurate for Asian or African populations.
Despite these flaws, BMI remains the primary triage tool for doctors simply because it is fast, free, and non-invasive.