What is the History of Body Mass Index (BMI)?

What is the History of Body Mass Index (BMI)?

The history of Body Mass Index (BMI) is a journey from 19th-century “social physics” to 21st-century medical controversy.

Whilst it is the most common health metric in the world, its origins reveal that it was never actually intended for medical diagnosis.

1. The Origins: The “Quetelet Index” (1830–1850)

The formula for BMI – weight (kg) / height (m2) – was created by Adolphe Quetelet, a Belgian polymath.

• The “Average Man”: Quetelet was not a doctor; he was a statistician. He wanted to define the “l’homme moyen” (the average man) as a social ideal.

• Mathematical Finding: He noticed that in adults, weight does not increase in direct proportion to height, but rather to the square of the height.

• The Bias: Quetelet’s data was based almost exclusively on White European men. He used these “averages” to define what he considered “normal” or “ideal” bodies, which later influenced the early eugenics movement.

2. The Rebrand: Ancel Keys and the 1972 Shift

For over a century, the formula remained a niche statistical tool. It wasn’t called “BMI” until 1972.

• Ancel Keys: An American physiologist published a landmark study of 7,400 men across seven countries. He concluded that Quetelet’s formula was the best proxy for body fat percentage in large populations.

• The Name Change: Keys officially coined the term “Body Mass Index” to replace the “Quetelet Index.”

• Population vs. Individual: Crucially, Keys warned that while BMI was great for studying groups (like 10,000 people), it was not necessarily a reliable tool for diagnosing individual health.

3. The “Overnight” Obesity Epidemic (1995–1998)

In the late 1990s, the definitions of “healthy” weight changed drastically, literally making millions of people “overweight” overnight.

• WHO Standardisation (1995): The World Health Organization officially adopted BMI as the global standard for obesity.

• The NIH Shift (1998): Following WHO guidelines, the U.S. National Institutes of Health (NIH) lowered the “Overweight” threshold from BMI 27.8 to BMI 25.0.

  • The Result: Approximately 25 to 30 million Americans who were considered “normal” on Monday were medically “overweight” by Tuesday.

4. Modern Milestones (2000s–2026)

In recent years, the medical community has shifted toward Precision Medicine, acknowledging that BMI is a “blunt instrument.”

• 2004: The WHO acknowledges that Asian populations have higher risks for diabetes at lower BMIs, leading to the adoption of ethnic-specific thresholds (e.g., Overweight starting at BMI 23).

• 2023: The American Medical Association (AMA) officially adopts a new policy stating that BMI should not be used alone for clinical diagnosis due to its historical harm and inability to account for muscle mass or racial body composition differences.

• 2025–2026: Leading health organizations (like NICE in the UK) updated official statistics to correct “misclassification errors.” In 2025, it was estimated that 1 million minority ethnic adults in England were being wrongly classified as ‘healthy’ because doctors weren’t using the lower, ethnicity-adjusted BMI thresholds.

Summary of Key Dates

The Evolution of BMI Criticism

Today, BMI is increasingly viewed as a screening tool, not a diagnostic tool. In 2026, healthcare providers are encouraged to look “Beyond BMI” by using:

1. Waist-to-Height Ratio: Better at predicting heart disease.

2. DEXA Scans: The “gold standard” for measuring actual body fat vs. muscle.

3. Metabolic Health Markers: Blood pressure, A1C, and cholesterol levels.