A newly proposed body mass index aligned more closely with waist-to-height ratio than existing alternatives, offering a promising new approach to assessing body size. However, larger studies are still needed before it can be adopted in clinical practice.
Study: Development of a consistent body mass index. Image credit: New Africa/Shutterstock.com
A recent Scientific Reports study developed the Consistent Body Mass Index (CBMI) and evaluated how closely it corresponded with waist-to-height ratio in a sample of 400 healthy participants, proposing CBMI as a comprehensive, scalable metric for assessing anthropometric status and estimating ideal body weight.
Why scientists are searching for better body metrics
In his seminal work L'homme moyen, Adolphe Quetelet, the Belgian polymath, introduced the concept of Body Mass Index (BMI), defined as body mass divided by height squared (kg/m²). Despite its widespread adoption, BMI exhibits major limitations: it is not valid for children, youth, or individuals at height extremes, and its dimensional nature (kg/m²) precludes scalability across populations.
These limitations have prompted the proposal of alternative indices, including the Corpulence Index (CI), Ponderal Index (PI), and Tri-ponderal Mass Index (TMI; mass/height³), which, while non-dimensional and somewhat improved, remain insufficient for general application.
Trefethen suggested a modified BMI (1.3 m/h^2.5), but this approach still suffers from dimensionality flaws. The World Health Organization (WHO) now prioritizes waist circumference and waist-to-hip ratio as anthropometric markers for metabolic and cardiovascular risk, diabetes, cancer, and mortality.
BMI and waist circumference remain central to risk stratification, yet their dimensional characteristics compromise reliability across body sizes; for instance, a waist circumference of 0.90 m cannot be interpreted equivalently for individuals of different heights. This highlights the need for robust, non-dimensional measures to enable consistent risk classification.
Recent studies increasingly support non-dimensional measures, particularly waist-to-height ratio, for predicting health risks and obesity-related outcomes. However, the mechanistic and comparative validity of these indices, particularly relative to directly measured adiposity, remains underexplored. A universally applicable body index should be non-dimensional and relate to geometric proportions such as the waist-to-height (w/h) ratio.
Researchers develop a new scalable body size index
This study introduces the CBMI, a newly proposed anthropometric index designed to provide a more scalable way to assess body size across different ages and body sizes than conventional BMI. Rather than relying solely on weight and height, the new index was mathematically derived to align closely with the waist-to-height ratio, a measure increasingly associated with obesity-related health risks.
To develop the index, the researchers created a simplified mathematical model of the human body, representing it as a cylinder whose height matched a person's stature and whose circumference reflected waist size. Although this approach cannot fully capture differences in body shape, sex, ethnicity, or body composition, the authors considered it a practical framework for developing and testing the new index.
The researchers then compared CBMI with the existing Tri-ponderal Mass Index (TMI), another height-adjusted alternative to BMI, to determine which better reflected waist-to-height ratio. Across their dataset, CBMI showed a stronger correspondence with the waist-to-height ratio than TMI, suggesting it may provide a more consistent way to classify anthropometric status.
To evaluate the approach, the team collected standardized measurements of weight, height, and waist circumference from 400 healthy participants, including infants, children, adolescents, and adults recruited through a single hospital in Istanbul. Participants were grouped by age and sex to assess whether the index could be applied across different life stages. However, the authors emphasized that the study represents an initial evaluation and that larger, more representative studies are needed before the findings can be generalized to broader populations.
CBMI classifications closely matched waist-to-height measurements
Using data from the study and evidence from previous research, the team proposed preliminary classification thresholds for both waist-to-height ratio and CBMI. Although the average waist-to-height ratio in the study population was 0.50, the researchers stressed that this should not be regarded as an ideal value because rising body weight worldwide is likely to have shifted population averages upward.
Instead, they proposed 0.50 as the upper limit of the normal range and 0.46 as an ideal reference value, while noting that these cut-offs are tentative and require validation in larger, more representative populations. The proposed thresholds were intended for all age groups except infants younger than one year, whose body proportions differ from those of older children and adults.
The researchers also developed corresponding CBMI categories that closely matched the proposed waist-to-height ratio ranges. Because the two measures classified participants in a similar way, the authors suggest that CBMI could provide a practical alternative for assessing anthropometric status. However, they emphasize that these categories remain provisional until they are tested in broader populations.
To illustrate the approach, the paper describes a 10-year-old girl weighing 40 kg, standing 147 cm tall, and with a waist circumference of 67 cm. Under the proposed system, both her waist-to-height ratio and CBMI placed her close to the authors' ideal range. By contrast, the paper compares her BMI with adult BMI thresholds, although BMI in children is normally interpreted using age- and sex-specific reference charts.
The example highlights how CBMI and waist-to-height ratio can classify body size differently from conventional BMI, but the study did not validate the new index against direct measures of body fat or clinical outcomes, so further research will be needed to establish its clinical value.
CBMI shows promise but requires further validation
The findings suggest that CBMI could offer a more consistent way of assessing anthropometric status across different ages and body sizes than conventional BMI, as it aligns more closely with the waist-to-height ratio. The researchers also propose that the index could be used to estimate ideal body weight for a given height.
However, they caution that these findings represent an early step rather than a validated clinical tool. The proposed classification thresholds remain preliminary, and further studies comparing CBMI with direct measures of body fat, metabolic health, and disease outcomes will be needed before it can be considered for routine clinical or public health use.
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