BRI vs height (vertical axis) vs waist circumference (horizontal axis)
Body roundness index (BRI) is a calculated geometric index used to quantify an aspect of 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]
Introduced in 2013, the BRI calculation can be used to estimate total and visceralbody 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 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– indicating wider, rounder bodies– were found to have a risk of all-cause mortality that was increased by up to 49% compared to people having a medium BRI of 5.[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 3 or less (midsection leanness) to 7 or more (midsection roundness), with a medium index of about 5.[1][3] As a relatively newer predictive metric, BRI has a smaller research record compared to long-established indices like the BMI and 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 in some countries.
History
BRI was first reported in 2013 by the mathematician Diana Thomas and colleagues in an analysis of three databases from studies of demographics, anthropometrics, fat mass, and visceral fat volume.[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 × Eccentricity
Range of body roundness
Body roundness shapes vary across a range of people who are lean (BRI less than 3) to severely obese (BRI more than 12).[1] According to the authors who developed BRI and subsequent research, overlap between adjacent BRI categories may occur.[1][3]
Calculation
Derivation of the BRI formula
1.
h: the subject's height, c: waist circumference.
2.
A cylinder with the same height and circumference.
3.
e: eccentricity of the largest ellipse fitting its side view.
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 height.
An automatic calculator computes the BRI using waist, height and an ellipse factor.[1][2] 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 / (2π)]2 / [0.5 × height2) which simplifies as follows.
Waist circumference and height can be in any unit of length, as long as they both use the same one.[1][3]
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.[1]
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.[1] The maximum observed BRI value in the NHANES data was 16.[1][3]
BRI had similar accuracy in predicting percentage body fat and percentage 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 and five other metrics – 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]
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]
See also
Allometry– Study of the relationship of body size to shape, anatomy, physiology, and behavior
Body mass index (BMI) is a value derived from the mass (weight) and height of a person. The BMI is defined as the body mass divided by the square of the body height, and is expressed in units of kg/m2, resulting from mass in kilograms (kg) and height in metres (m).
Metabolic syndrome is a clustering of at least three of the following five medical conditions: abdominal obesity, high blood pressure, high blood sugar, high serum triglycerides, and low serum high-density lipoprotein (HDL).
Abdominal obesity, also known as central obesity and truncal obesity, is the human condition of an excessive concentration of visceral fat around the stomach and abdomen to such an extent that it is likely to harm its bearer's health. Abdominal obesity has been strongly linked to cardiovascular disease, Alzheimer's disease, and other metabolic and vascular diseases.
Adipose tissue is a loose connective tissue composed mostly of adipocytes. It also contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular endothelial cells and a variety of immune cells such as adipose tissue macrophages. Its main role is to store energy in the form of lipids, although it also cushions and insulates the body.
The waist is the part of the abdomen between the rib cage and hips. Normally, it is the narrowest part of the torso.
The waist–hip ratio or waist-to-hip ratio (WHR) is the dimensionless ratio of the circumference of the waist to that of the hips. This is calculated as waist measurement divided by hip measurement. For example, a person with a 75 cm waist and 95 cm hips has WHR of about 0.79.
The body fat percentage of an organism is the total mass of its fat divided by its total body mass, multiplied by 100; body fat includes essential body fat and storage body fat. Essential body fat is necessary to maintain life and reproductive functions. The percentage of essential body fat for women is greater than that for men, due to the demands of childbearing and other hormonal functions. Storage body fat consists of fat accumulation in adipose tissue, part of which protects internal organs in the chest and abdomen. A number of methods are available for determining body fat percentage, such as measurement with calipers or through the use of bioelectrical impedance analysis.
Sagittal abdominal diameter (SAD) is a measure of visceral obesity, the amount of fat in the gut region. SAD is the distance from the small of the back to the upper abdomen. SAD may be measured when standing or supine. SAD may be measured at any point from the narrowest point between the last rib and the iliac crests to the midpoint of the iliac crests.
Human body shape is a complex phenomenon with sophisticated detail and function. The general shape or figure of a person is defined mainly by the molding of skeletal structures, as well as the distribution of muscles and fat. Skeletal structure grows and changes only up to the point at which a human reaches adulthood and remains essentially the same for the rest of their life. Growth is usually completed between the ages of 13 and 18, at which time the epiphyseal plates of long bones close, allowing no further growth.
The Corpulence Index (CI) is a measure of corpulence, or of leanness in other variants, of a person calculated as a relationship between mass and height. It was first proposed in 1921 as the "Corpulence measure" by Swiss physician Fritz Rohrer and hence is also known as Rohrer's Index. It is similar to the body mass index, but the mass is normalized with the third power of body height rather than the second power. In 2015, Sultan Babar showed that CI does not need to be adjusted for height after adolescence.
Sarcopenic obesity is a combination of two disease states, sarcopenia and obesity. Sarcopenia is the muscle mass/strength/physical function loss associated with increased age, and obesity is based off a weight to height ratio or body mass index (BMI) that is characterized by high body fat or being overweight.
Female body shape or female figure is the cumulative product of a woman's bone structure along with the distribution of muscle and fat on the body.
Obesity classification is a ranking of obesity, the medical condition in which excess body fat has accumulated to the extent that it has an adverse effect on health. The World Health Organization (WHO) classifies obesity by body mass index (BMI). BMI is further evaluated in terms of fat distribution via the waist–hip ratio and total cardiovascular risk factors. In children, a healthy weight varies with sex and age, and obesity determination is in relation to a historical normal group.
Android fat distribution describes the distribution of human adipose tissue mainly around the trunk and upper body, in areas such as the abdomen, chest, shoulder and nape of the neck. This pattern may lead to an "triangle"-shaped body or central obesity, and is more common in males than in females. Thus, the android fat distribution of men is about 48.6%, which is 10.3% higher than that of premenopausal women. In other cases, an ovoid shape forms, which does not differentiate between men and women. Generally, during early adulthood, females tend to have a more peripheral fat distribution such that their fat is evenly distributed over their body. However, it has been found that as females age, bear children and approach menopause, this distribution shifts towards the android pattern of fat distribution, resulting in a 42.1% increase in android body fat distribution in postmenopausal women. This could potentially provide evolutionary advantages such as lowering a woman's center of gravity making her more stable when carrying offspring.
The body adiposity index (BAI) is a method of estimating the amount of body fat in humans. The BAI is calculated without using body weight, unlike the body mass index (BMI). Instead, it uses the size of the hips compared to the person's height.
The waist-to-height ratio is the waist circumference divided by body height, both measured in the same units.
TOFI (thin-outside-fat-inside) is used to describe lean individuals with a disproportionate amount of fat stored in their abdomen. The figure to illustrate this shows two men, both 35 years old, with a BMI of 25 kg/m2. Despite their similar size, the TOFI had 5.86 litres of internal fat, whilst the healthy control had only 1.65 litres.
A Body Shape Index (ABSI) or simply body shape index (BSI) is a metric for assessing the health implications of a given human body height, mass and waist circumference (WC). The inclusion of WC is believed to make the BSI a better indicator of risk of mortality from excess weight than the standard body mass index. ABSI correlates only slightly with height, weight and BMI, indicating that it is independent of other anthropometric variables in predicting mortality.
Normal weight obesity is the condition of having normal body weight, but with a high body fat percentage, leading to some of the same health risks as obesity.
Relative Fat Mass (RFM) is a simple formula for the estimation of overweight or obesity in humans that requires only a calculation based on a ratio of height and waist measurements.
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