Health care professionals have a new tool in their medical kits for assessing the health of their patients. The Body Roundness Index has the promise of overcoming several of the weaknesses of the long-established Body Mass Index (BMI), which has often been misused as a health indicator by the profession.

BMI has become entrenched in large part because it has two basic inputs that are easy to measure: height and weight. These two factors are combined in a mathematical formula to provide a single value to indicate how relatively healthy an individual is based on just their weight and height. Or would if it were used appropriately.

Like BMI, the Body Roundness Index (BRI) has simple inputs that can be easily obtained using standard height gauges and measuring tapes: height and waist circumference. The Conversation describes how it came about and its potential:

BRI was developed by US researchers in 2013 in response to criticisms of BMI. Instead of looking at height and weight, BRI mathematically quantifies body fat levels by looking at height and waist circumference instead. This provides a value typically ranging from one to 20. It is the lowest and highest values that suggest the highest health risk.

Numerous studies have shown that BRI may be better than BMI at predicting the health risks associated with different levels of body fat. This includes predicting risk of weight-related diseases such as cardiovascular disease, diabetes, kidney disease and cancer, as well as death from any cause.

This latest study, which looked at 32,995 US adults between 1999 and 2018, found an association between BRI and death from any cause. Specifically, they also found that people with the lowest and highest BRI scores had the greatest health risks.

They also found that BRI was better than BMI at accurately detecting this risk. This is because BRI considers the fat held around the abdomen, which is linked to greater risk of health problems. This is different to BMI, which only considers overall weight.

BRI has the potential to be a better indicator of an individual's relative health than BMI while also being far less expensive, especially when compared with the alternative of today's more exact medical scanning and sensing technologies. And while's there's an online tool that can calculate your BRI, it's a little clunky to use. Especially if you want to run a number of "what if" scenarios in short order, like you would if you wanted to find out where it sets the boundary between being in or out of what it identifies as "the healthy zone" for someone of your height.

Which is to say we think there's room in the tool marketplace for a simpler, more bare bones tool to do the math. So we built it. Just enter the indicated measurements and the tool will do the math. If you're accessing this article on a site that republishes our RSS news feed, please click through to our site to access a working version.

As you can see, our tool is as bare bones as it gets. As a bonus, because of the underlying math, we don't have to worry about the units of measurement, provided they are the same. Use inches for both your height and waist circumference, you're good to go. The same is true if you use centimeters for both. Or cubits, if you must. The only limitation is you can't mix and match units and expect to get reliable results.

Now that you have the result for what you entered, what might it tell you?

That's where the long term study of Americans' health comes into play. The following chart presents all-cause mortality based on BRI for the individuals included in the study from 1999 through 2019. Find your BRI on the horizontal axis, then look up to see where the U-shaped curve puts your relative risk of death compared to where the minimum risk is at the lowest point of the curve.

In this chart, the solid blue curved line is the estimate of all-cause mortality for individuals with the Body Roundess Index indicated in the horizontal axis, and the light blue shading represents the 95% confidence interval for each level.

Here's what the authors have to say about what the chart shows:

As an extension, we expanded NHANES cycles from 1999 through 2018 and followed up to December 31, 2019, and we observed a U-shaped risk trajectory for the association between BRI and all-cause mortality. Differing from the study by Zhou et al, we chose the middle quantile (BRI, 4.5-5.5) of this U-shaped trajectory as the reference and found that all-cause mortality risk was increased by 25% for adults with BRI less than 3.4 and by nearly 50% for adults with BRI 6.9 or greater. The magnitude of risk estimation persisted even after excluding accidental deaths or deaths within 2 years or reserving participants with myocardial infarction, stroke, congestive heart failure, or cancer. Hence, estimates of mortality risk associated with BRI may help inform decision-making in clinical settings.

In this national cohort, 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. 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. The reasons behind the association between BRI and mortality may be epidemiologically and clinically plausible. 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 an increased risk of cardiometabolic diseases, even among participants with weight within reference range.

Aside from its potential as a better-than-BMI health indicator, BRI also caught our attention because the math behind incorporates the formula for the eccentricity of an ellipse. Which you can see if you look closely at our AI-generated version of DaVinci's Vitruvian Man sketch.

References

Zhang X, Ma N, Lin Q, et al. Body Roundness Index and All-Cause Mortality Among US Adults. JAMA Netw Open. 2024;7(6):e2415051. DOI: 10.1001/jamanetworkopen.2024.15051.

Thomas, DM; Bredlau, C; Bosy-Westphal, A;  et al.  Relationships between body roundness with body fat and visceral adipose tissue emerging from a new geometrical model. Obesity (Silver Spring). 2013;21(11):2264-2271. DOI: 10.1002/oby.20408.

Image Credit: Microsoft Copilot Designer.. Prompt: "Vitruvian Man with an ellipse as long as the man is tall and as wide as the man's waist".