Why BMI is a Flawed Tool For Measuring Body Composition
Imagine two people side by side. One is an athlete and, the other rarely exercises, yet the Body Mass Index (BMI) chart shows that they’re both “overweight.” How is it possible that you’re both the same BMI? This is exactly the question I was asking when I saw my doctor last month. How is it possible that I’m overweight when I work out five days a week, watch what I eat, and can’t pinch a lot of skin? It seemed like I would always be classified as overweight even as I kept building muscle. This took me down a research rabbit hole that lasted two days. Here’s what I learned.
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How BMI is Calculated
BMI is calculated using a person’s weight and height. Here’s the formula:
- Multiply your weight in pounds by 703
- Divide that number by your height in inches
- Divide the result by your height in inches once more (which is the same as dividing by height squared).
You can use this calculator to check your BMI.
What Are Standard BMI Categories?
Based on your above BMI number, these are the BMI categories:
- Underweight is below 18.5
- Healthy Weight is 18.5 to 24.9
- Overweight is 25.0 to 29.9
- Obese is 30.0 or higher
Why is BMI Used?
For decades, BMI has been treated as the gold standard for measuring health. Doctors use it. Insurance companies use it. Many gyms and fitness folks use it. However, it misses the mark in so many areas. The invention of the BMI tool goes back to 1832 when Adolphe Quetelet, “a Belgian statistician, mathematician, and astronomer, was inspired by his passion for statistical analysis and bell-shaped curves to establish quantifiable characteristics of the normal man.” Then, physiologist Ancel Keys built upon his work in 1972 and coined the “body mass index” term. He supported the use of BMI through a study that analyzed 12 samples from 7,426 men considered “healthy.”
Think about that. The BMI tool was introduced in 1832 to record the body composition of “normal men.” Then it was officially adopted in 1972 because Keys studied 7,426 men who were considered “healthy.” It’s now 2026, and we’re still using a tool from decades ago that studied a small percentage of men. Men have very different body compositions than women, yet women are still being tested against them! I’m categorized as overweight because a very subjective tool is being used for men that was designed before I was even born!
Limitations of the BMI Tools & Why It’s Still Used
According to the Cleveland Clinic, BMI is used as a health screening tool because it is a quick, inexpensive, and easy-to-measure calculation that estimates a person’s body weight relative to their height. The problem with this is that it’s not an accurate measure of body fat or overall health. It doesn’t account for factors such as muscle mass, bone density, fat distribution, age, or sex. Because muscle is denser than fat, people with more muscle may weigh more without having excess body fat. If you’re active, lift weights, or play sports, the BMI tool can’t tell the difference between a fit person and someone who is sedentary and has health problems.
So, what are my takeaways from what initially felt like a very troubling number? I’m going to get a DEXA scan and VO2Max fitness test so I can look beyond my BMI number. But, the more concerning thing is that BMI is still used as a screening tool. Isn’t it time we focused on body composition (muscle mass, fat mass and distribution) to assess fitness and health? We shouldn’t have to seek this out on our own. Our doctors’ offices should have better measures!
