Body roundness index

Body roundess index (BRI) is a calculated geometric index used to quantify a person's individual body shape. Based on the principle of body eccentricity, it provides a rapid visual and anthropometric tool for health evaluation.^[1]

The BRI models the human body shape as an ellipse (an oval), with the intent to relate body girth with height to determine body roundness. It is calculated simply using a tape measure to obtain waist and hip circumference and height, which are then combined with an ellipse factor before computation by an automatic calculator.^[1][2]

Introduced in 2013, the BRI calculation can be used to estimate total and visceral body fat. Ranges of healthy body roundness have been established to accurately classify people with healthy fat mass (weight) compared to obese people who are at risk for morbidities.^[1]

Compared to conventional metrics, such as the body mass index (BMI), which uses only two metrics (weight and height), BRI may improve predictions of the amount of body fat and the volume of visceral adipose tissue. Despite its common use, BMI can misclassify individuals as obese because it does not distinguish between a person's lean body mass and fat mass. By comparison with BMI, BRI quantifies body girth in relation to height, potentially providing more accurate estimates of fat mass.

BRI scores could range from 1 to 15, with most people between 1 and 10, although those with scores of 6.9 and up — indicating the widest, roundest bodies — were found to have a risk of all-cause mortality that was increased by 49% in people with high BRI (considerable roundness) compared to a medium index.^[2][3] In a 2020 review, high BRI was associated with increased risk of metabolic syndrome and several other diseases.^[4]

Typical American adult BRI values range from 7 or more (considerable midsection roundness) to 3 or less (considerable midsection leanness), with a medium index of about 5.^[3] As a relatively newer predictive metric, BRI has a smaller research record compared to established indices like the BMI or waist-to-hip ratio, indicating its accuracy and uses remain to be fully established in clinical research.

BRI was first reported in 2013 by the mathematician, Diana Thomas and colleagues in an analysis of three databases containing results from demographic, anthropometric, fat mass, and visceral fat volume studies.^[1][2] Thomas visualized the human body shape as an egg or ellipse rather than as a cylinder envisioned in the concept of the BMI.^[1][2]

The degree of circularity of an ellipse is quantified by eccentricity, with values between 0 to 1, where 0 is a perfect circle and 1 is a vertical line.^[1] To accommodate human shape data in a greater range, Thomas and colleagues mapped eccentricity in a range of 1 to 20 by using the equation:^[1]

Body Roundness Index = 364.2 - 365.5 x Eccentricity

In using human body and fat mass data from the United States National Health and Nutrition Examination Survey (NHANES) database, the Thomas group found that BRI never was a negative value, and that larger BRI values were associated with people having a round shape, while shape values closer to 1 were related to people with narrow, lean bodies.^[1] The maximum observed BRI value in the NHANES data was 16.^[1]

The only device needed to determine BRI is a measuring tape for circumference of waist and determination of height.^[1][2] These values are factored with an eccentricity equation in a calculator.^[1][2]

BRI is calculated as 364.2 − 365.5  × √(1 − [waist circumference in cm / 2π]²  /  [0.5 × height in cm]²) which simplifies as follows.^[1][3]

${\displaystyle {\text{BRI}}=364.2-365.5{\sqrt {1-{\Big (}{\frac {\text{waist circumference in cm}}{\;\;\;\;\pi \;\;\;\;\;\times \;\;\;\;\;\,{\text{height in cm}}}}{\Big )}^{2}}}}$

The original study by Thomas and colleagues showed that the BRI, as a geometrically-derived index of body roundness, had similar accuracy in predicting % body fat and % fat volume as existing indices, such as the BMI.^[1]

As the conventional index associated with obesity research, the BMI has numerous drawbacks, as it is unable to distinguish between muscle and fat, is inaccurate in predicting body fat percentage, and has poor ability to predict the risk of heart attack, stroke or death.^[1][5]

In a comparison study with BMI, a body shape index, conicity index, body adiposity index, waist–hip ratio, and abdominal volume index (AVI), BRI and AVI proved most effective at predicting risk of developing nonalcoholic fatty liver disease (NAFLD).^[6] BRI and AVI also accurately stratified diagnosis of NAFLD by race, age, and gender.^[6]

BRI was compared to the waist-to-height ratio to estimate the percentage of body fat and visceral adipose tissue, and was found to be a superior index of physical health status.^[5]

The BRI has proved effective as an index for identifying risk of death from different diseases,^[3] disorders of metabolic syndrome,^[4][5][7] cardiovascular diseases in association with sarcopenia,^[8] and bone mineral density.^[9] BRI was also a better indicator than the BMI and body shape index for predicting the risk of hypertension, dyslipidemia, and hyperuricemia in Chinese women.^[5]

Other indices of body and fat mass, such as BMI and waist-to-height ratio, have undergone more research evaluation and longitudinal clinical applications than BRI, and may be better predictors of fat distribution (e.g., visceral vs. subcutaneous fat) for estimating health risks.^[10][11]

Two measurements of the BRI – waist circumference and hip circumference – are subject to high variability in standing obese people.^[1] Such variability may indicate differences in fat distribution in people with excessive visceral fat, causing errors in BRI.^[1][3]

Diagnostic factors for diseases associated with obesity, such as ethnicity, family history, dietary habits, and physical activity, are not factored into the BRI, or are other outcomes, such as organ health status and duration of disease.^[3][7]

• Allometry – Study of the relationship of body size to shape, anatomy, physiology, and behavior
• Body shape index – Human health index
• History of anthropometry – Historical uses of anthropometry
• Normal weight obesity – Metabolically obese normal weight
• Relative fat mass – Ratio-based formula for estimating obesity in humans