New body mass index could outperform BMI and be used from infancy to adulthood

Researchers have developed a new body mass index that may provide a more accurate assessment of body size than the traditional Body Mass Index (BMI), while also being applicable across all age groups—from newborns to older adults.

The new measure, called the Consistent Body Mass Index (CBMI), was presented in Scientific Reports. Unlike conventional BMI, which assumes body weight increases in proportion to height squared, CBMI is based on the principle that the human body is a three-dimensional structure and therefore weight should scale with height cubed.

Using a mathematical model that represents the body as a cylinder, the researchers created a formula that incorporates body weight, height and waist circumference to better reflect overall body proportions.

To evaluate the new index, scientists studied 400 participants in Istanbul, ranging in age from one-day-old newborns to 75-year-old adults. The participants were evenly divided into four groups: adult men, adult women, boys and girls.

The analysis showed that CBMI closely corresponded to the waist-to-height ratio, an established indicator of obesity-related health risks. Across the entire study population, the correlation coefficient reached 0.837, suggesting a strong relationship. The association was strongest among children and somewhat weaker among adult men.

BMI has been widely used for nearly 200 years because it is simple to calculate using height and weight. However, experts have increasingly criticized the index because it does not account for differences in age, sex, ethnicity, body composition or fat distribution. It may therefore misclassify muscular individuals, older adults, children, and people who are exceptionally tall or short.

One proposed alternative, the Tri-ponderal Mass Index (TMI), already uses height cubed instead of height squared and has shown some advantages over BMI. However, previous studies found that TMI also performs inconsistently across different age groups.

The researchers argue that waist circumference provides valuable information about metabolic health because it is associated with conditions such as cardiovascular disease, hypertension, type 2 diabetes and several cancers. However, waist circumference alone is also influenced by body size.

To overcome these limitations, the scientists focused on the waist-to-height ratio and introduced an additional "form factor" to account for natural variations in body shape rather than assuming every person has the same body geometry.

Using statistical analyses, the team compared CBMI, BMI and TMI with the participants' actual body measurements. CBMI demonstrated the greatest consistency across different ages and body types.

Based on these findings, the researchers developed preliminary classification charts that include proposed thresholds for normal weight, overweight and obesity.

The authors caution that the new index still requires validation in larger and more diverse populations before it can replace BMI in routine clinical practice. Additional studies will be needed to confirm the proposed cut-off values and determine how well CBMI predicts future health outcomes.

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