Is the BMI index 'outdated'?

Body mass index (BMI) has long been used as a medical screening tool. It is one of the most popular but also controversial health metrics because it is used to classify people as overweight, obese, or extremely obese.

BMI is not accurate?

Developed nearly 200 years ago, the original BMI formula was based on data from men, mostly white, and was not designed for medical screening. It also did not take into account factors such as fat and muscle ratio, bone density, or racial and gender differences.

In fact, some people with a normal BMI have a high percentage of body fat and low muscle mass, while people with a high BMI may have more muscle. Because muscle is 10% to 20% denser than fat, two people of the same height and weight but with different bodies can look very different.

This is because BMI does not differentiate between muscle and fat. For example, athletes can be heavy because of their greater muscle mass. They will have a high BMI but a normal waist measurement.

Research has also shown the limitations of BMI. A 2016 study analyzed the relationship between BMI and blood pressure and blood tests.

BMI is used as a medical screening tool.

The study found that nearly half of people with a BMI of 25 to 29.9 (classified as overweight or obese) and nearly a third of people with a BMI of 30 or higher (classified as obese) were actually metabolically healthy. In contrast, 30 percent of all people with a BMI of 18.5 to 24.9 (considered a healthy weight) were metabolically unhealthy.

The Rise of BRI

A new index, called the body roundness index (BRI), is gaining attention as an alternative to BMI. As its name suggests, the BRI measures body "roundness" based on height and waist circumference, regardless of 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 the organs and hinders their function.

Fat that accumulates in the abdominal cavity poses a much higher risk of disease than fat that accumulates around the hips, thighs or buttocks.

The BRI was developed by mathematician Diana Thomas, a professor at the United States Military Academy at West Point, New York. She first introduced the index in a 2013 paper in the journal Obesity. While BMI uses a cylinder as its model, the BRI is based on an oval.

Diana Thomas said she got the idea when she looked in the mirror and realized that her body was more egg-shaped than cylindrical. Diana Thomas applied a mathematical concept called eccentricity to create the formula for calculating BRI.

The more circular a person's body shape is, 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 take into account a person's muscle mass, which plays an important role in health.

According to American nutritionist Maya Feller, although BRI and BMI can be helpful, people should rely on tests to assess internal health rather than weight or measurements.

'I always wanted to check inside my body. You might look great on the outside, but what are your lipids, blood pressure, and blood sugar? Those are the things I want to know . '