View source for Body roundness index

{{Short description|Body scale based on waist circumference and height}}
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{{Use American English|date=September 2024}}
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{{Infobox diagnostic
| name = Body roundness index
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| image = body_roundness_index_graph.svg
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| caption = BRI vs height (vertical axis) vs<br />waist circumference (horizontal axis)
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{{Human body weight}}

'''Body roundness index''' ('''BRI''') is a calculated [[Geometry|geometric]] index used to quantify an aspect of a person's individual [[body shape]]. Based on the principle of body [[Eccentricity (mathematics)|eccentricity]], it provides a rapid visual and [[anthropometry|anthropometric]] tool for health evaluation.<ref name="thomas">{{cite journal |vauthors=Thomas DM, Bredlau C, Bosy-Westphal A, Mueller M, Shen W, Gallagher D, Maeda Y, McDougall A, Peterson CM, Ravussin E, Heymsfield SB |title=Relationships between body roundness with body fat and visceral adipose tissue emerging from a new geometrical model |journal=Obesity |volume=21 |issue=11 |pages=2264–71 |date=November 2013 |pmid=23519954 |pmc=3692604 |doi=10.1002/oby.20408}}</ref>

Introduced in 2013, the BRI calculation can be used to estimate total and [[Organ (biology)#Viscera|visceral]] [[Adipose tissue|body fat]]. Ranges of healthy body roundness have been established to accurately classify people with healthy fat [[mass]] ([[Mass versus weight|weight]]) compared to [[obese]] people who are at risk for [[morbidity|morbidities]].<ref name=thomas/>

Compared to traditional metrics, such as the [[body mass index]] (BMI), (which uses 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. Instead, BRI quantifies body girth as well as height, potentially providing more accurate estimates of fat mass.

BRI scores range from 1 to 16, with most people between 1 and 10, although people with scores of 6.9 and up&nbsp;– indicating wider, rounder bodies&nbsp;– were found to have a risk of [[Mortality rate|all-cause mortality]] that was increased by up to 49% compared to people having a medium BRI of 5.<ref name="rabin">{{cite news |first=Roni Caryn|last=Rabin |title=Time to Say Goodbye to the B.M.I.? |url=https://www.nytimes.com/2024/09/06/health/body-roundness-index-bmi.html |access-date=21 September 2024 |work=The New York Times |date=6 September 2024}}</ref><ref name="zhang">{{cite journal |vauthors=Zhang X, Ma N, Lin Q, Chen K, Zheng F, Wu J, Dong X, Niu W |title=Body roundness index and all-cause mortality among US adults |journal=JAMA Network Open |volume=7 |issue=6 |pages=e2415051 |date=June 2024 |pmid=38837158 |pmc=11154161 |doi=10.1001/jamanetworkopen.2024.15051}}</ref> In a 2020 review, high BRI was associated with increased risk of [[metabolic syndrome]] and several other diseases.<ref name="rico">{{cite journal |vauthors=Rico-Martín S, Calderón-García JF, Sánchez-Rey P, Franco-Antonio C, Martínez Alvarez M, Sánchez Muñoz-Torrero JF |title=Effectiveness of body roundness index in predicting metabolic syndrome: A systematic review and meta-analysis |journal=Obesity Reviews|volume=21 |issue=7 |pages=e13023 |date=July 2020 |pmid=32267621 |doi=10.1111/obr.13023 |url=https://onlinelibrary.wiley.com/doi/full/10.1111/obr.13023}}</ref>

Typical American adult BRI values range from 3 or less (midsection leanness) to 7 or more (midsection roundness), with a medium index of about 5.<ref name=thomas/><ref name=zhang/> As a relatively newer predictive metric, BRI has a smaller research record compared to long-established indices like the BMI and [[Waist–hip ratio|waist-to-hip ratio]], so its accuracy and applications remain to be as fully established. Conversely, the simple [[waist-to-height ratio]] (which uses the same measurements and is simpler to calculate) has a better research base, leading to its adoption as the preferred guideline [[waist-to-height ratio#Guidelines|in some countries]].

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==History==
BRI was first reported in 2013 by the mathematician [[Diana Thomas (mathematician)|Diana Thomas]] and colleagues in an analysis of three databases from studies of [[Demography|demographics]], anthropometrics, fat mass, and visceral fat volume.<ref name=thomas/><ref name=rabin/> Thomas visualized the human body shape as an egg or ellipse rather than as the [[cylinder]] model that is envisioned in the concept of the BMI.<ref name=thomas/><ref name=rabin/>

The degree of circularity of an ellipse is quantified by eccentricity, with values between 0 to 1, where 0 is a perfect circle (waist circumference same as height) and 1 is a vertical line.<ref name=thomas/> 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:<ref name=thomas/>

{{in5}} Body Roundness Index = 364.2 − 365.5 × ''Eccentricity''

==Range of body roundness==
Body roundness shapes vary across a range of people who are lean (BRI less than 3) to [[Obesity#Classification|severely obese]] (BRI more than 12).<ref name=thomas/> According to the authors who developed BRI and subsequent research, overlap between adjacent BRI categories may occur.<ref name=thomas/><ref name=zhang/>

==Relationship to other anthropometric indices==

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.<ref name=thomas/> The maximum observed BRI value in the NHANES data was 16.<ref name=thomas/><ref name=zhang/>

BRI had similar accuracy in predicting percentage body fat and percentage fat volume as existing indices, such as the BMI.<ref name=thomas/> 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.<ref name=thomas/><ref name=tian/>

In a comparison study with BMI and five other metrics &ndash; a [[body shape index]], conicity index, [[body adiposity index]], waist–hip ratio, and abdominal volume index (AVI) &ndash; BRI and AVI proved most effective at predicting risk of developing [[nonalcoholic fatty liver disease]] (NAFLD).<ref name="tian23">{{cite journal |vauthors=Tian X, Ding N, Su Y, Qin J |title=Comparison of Obesity-Related Indicators for Nonalcoholic Fatty Liver Disease Diagnosed by Transient Elastography |journal=The Turkish Journal of Gastroenterology|volume=34 |issue=10 |pages=1078–1087 |date=October 2023 |pmid=37737216 |pmc=10645279 |doi=10.5152/tjg.2023.23101}}</ref> BRI and AVI also accurately stratified diagnosis of NAFLD by race, age, and gender.<ref name=tian23/>

==Clinical research==
The BRI has proved effective as an index for identifying risk of death from different diseases,<ref name=zhang/> disorders of metabolic syndrome,<ref name=rico/><ref name="tian">{{cite journal |vauthors=Tian S, Zhang X, Xu Y, Dong H |title=Feasibility of body roundness index for identifying a clustering of cardiometabolic abnormalities compared to BMI, waist circumference and other anthropometric indices: the China Health and Nutrition Survey, 2008 to 2009 |journal=Medicine |volume=95 |issue=34 |pages=e4642 |date=August 2016 |pmid=27559964 |pmc=5400331 |doi=10.1097/MD.0000000000004642}}</ref><ref name="liu">{{cite journal |vauthors=Liu Y, Liu X, Guan H, Zhang S, Zhu Q, Fu X, Chen H, Tang S, Feng Y, Kuang J |title=Body Roundness Index Is a Superior Obesity Index in Predicting Diabetes Risk Among Hypertensive Patients: A Prospective Cohort Study in China |journal=Frontiers in Cardiovascular Medicine |volume=8 |issue= |pages=736073 |date=2021 |pmid=34869638 |pmc=8638826 |doi=10.3389/fcvm.2021.736073|doi-access=free}}</ref> liver disease,<ref name=tian23/> [[cardiovascular disease]]s in association with [[sarcopenia]],<ref name="zhangx">{{cite journal |vauthors=Zhang X, Ding L, Hu H, He H, Xiong Z, Zhu X |title=Associations of Body-Roundness Index and Sarcopenia with Cardiovascular Disease among Middle-Aged and Older Adults: Findings from CHARLS |journal=The Journal of Nutrition, Health & Aging |volume=27 |issue=11 |pages=953–959 |date=2023 |pmid=37997715 |doi=10.1007/s12603-023-2001-2 |url=https://www.sciencedirect.com/science/article/pii/S1279770723026040|doi-access=free }}</ref> and [[bone mineral density]].<ref name="ding">{{cite journal |vauthors=Ding Z, Zhuang Z, Tang R, Qu X, Huang Z, Sun M, Yuan F |title=Negative association between Body Roundness Index and bone mineral density: insights from NHANES |journal=Frontiers in Nutrition |volume=11 |issue= |pages=1448938 |date=2024 |pmid=39176032 |pmc=11340502 |doi=10.3389/fnut.2024.1448938|doi-access=free}}</ref> 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.<ref name=tian/>

==Limitations==
[[File:waist_to_height_ratio_vs_body_roundness_index_graph.svg|thumb|
vertical axis: height,
horizontal axis: waist circumference,
dotted grey: WHtR
solid black: BRI 
]]
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.<ref name="zhang23">{{cite journal |vauthors=Zhang X, Li G, Shi C, Tian Y, Zhang L, Zhang H, Sun Y |title=Comparison of conventional and unconventional obesity indices associated with new-onset hypertension in different sex and age populations |journal=Scientific Reports |volume=13 |issue=1 |pages=7776 |date=May 2023 |pmid=37179428 |pmc=10182979 |doi=10.1038/s41598-023-34969-0|bibcode=2023NatSR..13.7776Z }}</ref><ref name="islam">{{cite journal|title=Anthropometric indices in predicting 10-year cardiovascular risk among males and females aged 40–74 years in south and southeast Asia: analysis of 12 WHO STEPS survey data|vauthors=Islam T, Chowdhuryb AT, Sirajb S| journal=The Lancet Regional Health, Southeast Asia|volume= 29|pages=100481|date=October 2024|doi=10.1016/j.lansea.2024.100481 |pmid=39315383 |pmc=11418002 }}</ref>

Two measurements of the BRI {{ndash}} waist circumference and hip circumference {{ndash}} are subject to high variability in standing obese people.<ref name=thomas/> Such variability may indicate differences in fat distribution in people with excessive visceral fat, causing errors in BRI.<ref name=thomas/><ref name=zhang/>

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.<ref name=zhang/><ref name=liu/>

==Calculation==
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. A simple [[tape measure]] suffices to obtain [[waist]] [[circumference]] and [[body height|height]].<ref name=thomas/><ref name=rabin/>
Waist circumference and height can be in any [[unit of length]], as long as they both use the same one.<ref name=thomas/><ref name=zhang/>

{{hatnote|The calculator (right or below) may be used to compute the [[Waist-height ratio]], [[Eccentricity (mathematics)|eccentricity]] and BRI automatically.}}
{{Body roundness index}}
BRI is calculated as 
<math display="block">\text{BRI}=364.2-365.5\sqrt{1-\Big(\frac{\text{waist circumference}}{\;\;\;\;\pi\;\;\;\;\;\times\;\;\;\;\;\,\text{height}}\Big)^2}</math> which can be broken down to 3 steps:
[[File:body_roundness_index_formula.svg|thumb|Derivation of the BRI formula
{|
|valign="top"|{{nowrap|1.}}||style="text-align:left;"|''h'': the subject's height, {{nowrap|''c'': waist circumference.}}
|-
|valign="top"|2.||style="text-align:left;"|A cylinder with the same {{nowrap|height and circumference.}}
|-
|valign="top"|3.||style="text-align:left;"|''e'': eccentricity of the largest {{nowrap|ellipse fitting}} its side view.
|}]]
# Compute Waist-to-height ratio, <math display="block">\text{WHtR}=\frac{\text{waist circumference}}{\text{height}}</math><br>= {{sfrac
|{{calculator|id=waistFormula1Inches|formula=waistinch|default=28|type=plain}} in 
|{{calculator|id=heightFormula1Feet|formula=heightfeet|default=5|type=plain}} ft {{calculator|id=heightFormula1Inch|formula=heightinches|default=3|type=plain}} in }}<br>= {{sfrac
|{{calculator|id=waistFormula1|formula=waistcm|default=72|type=plain}} cm
|{{calculator|id=heightFormula1|formula=heightcm|default=160|type=plain}} cm}}<br>{{=}} {{calculator|id=formula1Whtr|formula=waistcm/heightcm|default=0.45|type=plain}}
# Compute [[Eccentricity (mathematics)|eccentricity]] (e) of the vertical [[ellipse]] around the body, <math display="block">\text{e}=\sqrt{1-\Big(\frac{\text{WHtR}}{\pi}\Big)^2}</math><br>{{=}} sqrt(1-({{calculator|id=formula2Whtr|formula=formula1Whtr|default=0.45|type=plain}}/{{calculator|id=piFormula2|formula=pi|default=3.141592653589793|type=plain}})^2)<br>{{=}} {{calculator|id=formula2eccentricity|formula=sqrt(1-pow(formula1Whtr/piFormula2,2))|default=0.9896880621248427|type=plain}}
# Compute BRI, <math display="block">\text{BRI}=364.2-365.5\times\;\text{eccentricity}</math><br>{{=}} 364.3 - 365.5 * {{calculator|id=formula3eccentricity|formula=formula2eccentricity|default=0.9896880621248427|type=plain}}<br>{{=}} {{calculator|id=formula3bri|formula=364.2-365.5*formula3eccentricity|default=2.469013293369983|type=plain}} &asymp; {{calculator|id=formula3briRounded|formula=formula3bri|decimals=2|default=2.47|type=plain}}

Predictions of % total [[body fat]] and % [[visceral adipose tissue]] apply a different eccentricity equation  using waist and hip circumferences, age, height, gender, ethnicity, and body weight as inputs.<ref name=thomas/>

==See also==
*{{annotated link|Allometry}}
*{{annotated link|Body shape index}}
*{{annotated link|Classification of obesity}}
*{{annotated link|Corpulence index}}
*{{annotated link|History of anthropometry}}
*{{annotated link|Normal weight obesity}}
*{{annotated link|Relative fat mass}}
*{{annotated link|Waist–hip ratio}}
*{{annotated link|Waist-to-height ratio}}

==References==
{{reflist}}

[[Category:Anthropometry]]
[[Category:Body shape]]
[[Category:Classification of obesity]]
[[Category:Human body weight]]
[[Category:Human height]]
[[Category:Mathematics in medicine]]
[[Category:Medical signs]]
[[Category:Ratios]]