When we go to the hospital for a physical or to get medical treatment, we often see a number called Body Mass Index (BMI). It is calculated using height and weight to distribute people into underweight, healthy weight, overweight, and obesity. It is commonly used to tell us whether we are “healthy” or not.
But BMI is not a reliable measurement of health once we understand how it was created and what it leaves out.
~BMI Was Not Created for Individual Health~
BMI was originally developed in 1832 by Adolphe Quetelet, a Belgian statistician, not a doctor or medical researcher (Pray & Riskin, 2023). His goal was to study human bodies at a population level, not to evaluate individual health.
BMI was designed to be a simple number that was easy to collect and analyze for large groups of people.
A helpful way to think about this is shoe size. If we calculated the average shoe size of a population and labeled it as “normal,” it wouldn’t mean that everyone who wears a different size is unhealthy. Body size works the same way.
~BMI Is Based on a Narrow Sample~
In 1972, BMI was revised and popularized by physiologist Ancel Keys using data from 7,426 men (Pray & Riskin, 2023). Most of these participants were white, middle-aged men, with little representation of women or people from different ethnic and racial backgrounds.
Despite this limited sample, BMI is now used as a health measure for people of all genders, races, and body types.
It’s also important to note that the people who developed BMI were not medical clinicians, and BMI was never intended to diagnose health conditions in individual patients.
~BMI Leaves Out Important Parts of Health~
BMI is calculated using only height and weight. It does not measure many key aspects of health, including:
- Body fat percentage
- Muscle mass
- Fat Distribution
Because muscle weighs more than fat, people with higher muscle mass such as athletes or physically active individuals, may be labeled “overweight” or “obese” by BMI, even if they are metabolically healthy.
BMI also cannot identify visceral fat, which is fat stored around the internal organs and is more strongly linked to chronic disease risk than body weight alone.
~The Bottom Line~
BMI was never meant to measure individual health, and research continues to show its limitations. Health is shaped by many factors beyond height and weight, including genetics, access to healthcare, stress, nutrition, sleep, and environmental conditions. Trying to fit ourselves into a single number may not be the answer to improving health. Our bodies and our health are far more complex than BMI can capture.