Body Mass Index (BMI) has long been used as a medical screening tool. It is one of the most popular health metrics, yet it is also highly controversial because it is used to classify individuals as overweight, obese, or extremely obese.
Is BMI Inaccurate?
Developed nearly 200 years ago, the original BMI formula was based on data from men, primarily white individuals, and was not designed for medical screening. This index also does not take into account factors such as fat-to-muscle ratio, bone density, or differences in race and gender.
In reality, some individuals with a normal BMI may have high fat and low muscle ratios, while those with a high BMI may have more muscle mass. Since muscle is denser than fat by 10% to 20%, two people of the same height and weight but with different body compositions can look very different.
This is because BMI does not differentiate between muscle and fat. For example, athletes may weigh more due to their greater muscle mass. They might have a high BMI, but their waist measurements can still be normal.
Research has also highlighted the limitations of BMI. A 2016 study analyzed the relationship between BMI and blood pressure, as well as blood test results.
BMI is used as a medical screening tool.
The study found that nearly half of individuals with a BMI between 25 and 29.9 (classified as overweight or obese) and nearly one-third of those with a BMI of 30 or above (classified as obese) actually had good metabolic health. Conversely, 30% of the total population with a BMI between 18.5 and 24.9 (considered a healthy weight) had poor metabolic health.
The Rise of BRI
A new metric, known as Body Roundness Index (BRI), is gaining attention as an alternative to BMI. As its name suggests, BRI measures the “roundness” of the body based on height and waist circumference, without considering weight.
According to a study published in JAMA Network Open in June 2024, BRI may be more accurate than BMI in assessing obesity and related health risks.
Dr. Nick Fuller, a health and obesity expert at the University of Sydney (Australia), explains that waist measurement is a better indicator of visceral fat, the type of fat that accumulates in the abdominal cavity, which is considered the most dangerous because it surrounds organs and impairs their function.
Abdominal fat accumulation poses a much higher risk of disease compared to fat that accumulates around the hips, thighs, or buttocks.
BRI was developed by mathematician Diana Thomas, a professor at the United States Military Academy at West Point, New York. She first introduced this index in a 2013 paper published in the journal Obesity. While BMI uses a cylindrical model, BRI is based on an elliptical shape.
Diana Thomas mentioned that she came up with the idea when looking in the mirror and realizing that her body resembled an egg rather than a cylinder. She applied a mathematical concept called eccentricity to formulate the BRI.
The closer a person’s body shape is to a circle, the closer their BRI will be to 0; the more elongated or linear the body, the closer the BRI will be to 1.
BRI is not a perfect formula. Like BMI, BRI also does not account for an individual’s muscle mass, which plays a crucial role in health.
According to American nutritionist Maya Feller, while BRI and BMI can be useful, individuals should rely on tests that assess internal health rather than just weight or measurements.
“I always want to check inside the body. You may look great on the outside, but what about your lipids, blood pressure, and blood sugar? Those are the things I want to know.”
