The ubiquitous body mass index has a new anthropometric challenger – Body Roundness Index – a way to more accurately account for body shape.
Numerous studies have demonstrated that obesity as defined by BMI was significantly associated with elevated risk of all-cause mortality compared with BMI within the reference range.
However, it is widely recognized that body fat content cannot be characterized by BMI and among individuals with the same BMI, fat distribution and body composition varied dramatically.
To better embody fat distribution, a new measure, the Body Roundness Index (BRI), was coined by Thomas et al, who developed elliptical models based on human body shape to calculate body roundness and used eccentricity to estimate visceral fat and total body fat percentages.
Besides weight and height, BRI also considers waist circumference to reflect visceral fat distribution more comprehensively. BRI was found to be superior to other anthropometric indicators in estimating the risk for various clinical end points, including cardiometabolic disease, kidney disease, and cancer.
Furthermore, longitudinal studies have shown that high BRI was associated with the significantly increased risk of all-cause mortality and cardiovascular disease-specific mortality.
The current study, an international effort led by Dr Xiaoqun Dong from Brown University, included 32,995 adults, and evaluated the effectiveness of BRI against a survival outcome of all-cause mortality.
“For practical reasons, there remains a need for a simple and effective proxy indicator to better reflect visceral obesity. Accruing evidence indicates that BRI, as a newer anthropometric measure, can reflect visceral fat more comprehensively than conventional measures, including BMI,” Dr Dong said.
“Theoretically, assuming the shape of body as an ellipse with the long axis height and the short axis waist circumference, BRI can be calculated as the eccentricity of this ellipse via human modelling.”
Rather than apply the simplistic BMI formula (weight in kilograms divided by height in meters squared), BRI was calculated as 364.2 − 365.5 × √ (1 − [waist circumference in centimetres / 2π]2 / [0.5 × height in meters]2).
Due to the lack of a reference range, BRI was categorised into five groups according to the 20th, 40th, 60th, and 80th quantiles to explore the association with all-cause mortality, with the weighted association between BRI and all-cause mortality quantified using hazard ratios (HRs) with 95%CIs before and after adjusting for confounding factors.
“We noticed that very low BRI was associated with a significantly increased risk of all-cause mortality, especially in individuals aged 65 years and older,” Dr Dong explained.
“This association seems plausible, as BRI was identified as a potential proxy measure associated with nutritional status, and very low BRI can be accompanied with malnutrition, fatigue, reduced activity tolerance, and muscle atrophy.
“From epidemiological aspects, elevated BRI was significantly associated with an increased risk of cardiovascular and metabolic disorders, and even cancer, which might serve as the culprits responsible for all-cause mortality.
“From clinical aspects, the accumulation of visceral fat was associated with more profound insulin resistance and ands increased risk of cardiometabolic diseases, even among participants with weight within reference range.
“BRI experienced a stably increasing trend during nearly two decades, with a biennial change of 0.95%. It is hence reasonable to speculate BRI as a superior anthropometric measure for abdominal adiposity.”