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A new study suggests the body mass index (BMI)—which has been the standard tool used to classify overweight and obesity for decades—may soon have competition.
Researchers from Istanbul have developed a new measure called the Consistent Body Mass Index (CBMI).
According to the researchers, the new formula provides a more accurate way to assess body size across people of all ages, genders and body types.
The findings, published in Scientific Reports, challenge the key assumptions behind BMI that body weight scales with the square of a person’s height.
Simple But Flawed
BMI has been used in medicine and public health since the 19th century.
The simple formula was originally developed by Belgian mathematician Adolphe Quetelet to calculate body size by dividing weight by height squared.
Although simple and inexpensive to use, BMI has often been criticized for failing to distinguish between fat and muscle and for not accounting for differences in age, sex, ethnicity or body composition.
Factoring in the Waist
In the new study, researchers took a different approach by applying principles of geometry and physics.
The human body is a three-dimensional structure. For that reason, the researchers argue that body weight should scale more naturally with the cube of height rather than height squared.
Their resulting formula, CBMI = √(mass/height³), also incorporates body shape through its relationship with waist circumference.
The Research
To evaluate the new index, the researchers studied 400 people in Istanbul, including newborns, children and adults up to 75 years old.
Participants were divided into four groups of 100—adult men, adult women, boys and girls—and each person’s weight, height and waist circumference was measured.
The researchers compared CBMI with both the traditional BMI and the Tri-Ponderal Mass Index (TMI), another alternative that also uses height cubed.
They found CBMI showed the strongest relationship with waist-to-height ratio, a measurement widely regarded as a reliable indicator of obesity-related health risks.
Across all participants, CBMI achieved a correlation coefficient of 0.837, with the strongest performance among children.
Building on Previous Research
Previous research has linked waist circumference to the risk of cardiovascular disease, high blood pressure, Type 2 diabetes and several forms of cancer.
Newsweek previously covered research from 2020 that showed waist circumference was just as important as BMI in evaluating mortality risk, while a 2019 study found cognitive issues could be tied to larger waists.
The Turkish study authors say that while the findings are an early step and additional studies are necessary before CBMI can supplant BMI entirely as a routine practice, CBMI builds on the previous research while providing a measurement that remains consistent across different body sizes and life stages.
Based on their findings, the researchers also created new CBMI classification charts for normal weight, overweight and obesity and suggest the index could eventually be used to estimate ideal body weight from a person’s height.
Newsweek has reached out to the study authors for comment via email.
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