It’s not all that it’s hyped up to be

Body mass index (BMI) is a simple mathematical formula widely used to quickly gauge someone’s health. BMI = weight (kg) divided by height squared (m²). Its simplicity and cost-effectiveness makes BMI a popular health tool, but it’s based on some problematic logic.

Not a doctor

In the early 19th century, Belgian astronomer and mathematician Lambert Adolphe Quetelet was on a mission to find the “average man.”

He believed if he collected enough data on measurable characteristics such as weight and height, the average values would represent what the perfect human should be like.

Of course, Quetelet only collected data from Western European men.

During his studies, Quetelet saw a pattern between height and weight. In 1832, he created the “Quetelet index,” which is weight (kg) divided by height squared (m²).

One size fits all

In 1972, American physiologist Ancel Keys decided to find a simple method to predict an individual’s chances of developing a chronic disease.

He was inspired by the logic used by American health insurance companies to calculate their premiums.

Although Keys coined the term BMI, neither he nor Quetelet created BMI categories.

This was done by the World Health Organization following a 1995 report by an expert committee.

The BMI categories are:

• Underweight: BMI under 18
• Normal: BMI 18.5–24.9
• Overweight: BMI 25.0–29.9
• Obese: BMI over 30

These parameters are applied to all adults regardless of their race, age, sex, or other influential health conditions, like a physical disability.

A better weigh

Strange origins aside, medical professionals agree that the BMI’s biggest flaw is that it doesn’t differentiate fat from other forms of mass in the human body.

A professional athlete with low levels of body fat could have a BMI over 30 (obese) because of their high levels of muscle and bone mass, which is denser than fat.

Or an elderly person with very little muscle mass but high levels of fat could have a BMI within the normal or underweight range.

In both scenarios, the true health status of these individuals is incorrectly masked by their BMI.

Unlike BMI, there’s a proven correlation between an individual’s body fat percentage and their general health.

If an individual has most of their body fat stored around their belly, they have a higher risk of developing a chronic disease, which cannot be captured by someone’s overall weight.

Health professionals currently recommend measuring waist circumference as a far more accurate way to quickly gauge an individual’s health—not BMI.

Who’s behind this story?

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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