Should we ditch BMI and use 'body roundness index'?

Should we ditch BMI and use 'body roundness index'?


Since it was first used in the late 20th century, BMI has remained the most popular method of measuring health.

BMI has been the most popular way to measure health since it was first used in the late 20th century. | Photo Credit: Getty Images/iStockphoto

The body mass index (better known as BMI) has long been used to get a quick and easy snapshot of a person's body fat levels. To calculate a person's BMI, you multiply their weight in kilograms by their height in meters and divide that by 100 kg. The resulting number is used to determine a person's health risk.

Although there are much better ways to accurately measure a person's body fat levels – such as using dual-energy X-ray absorptiometry (DEXA) or magnetic resonance imaging (MRI) – these are very resource-intensive. This may explain why BMI has remained the preferred method for measuring health since it was first used in the late 20th century.

But many health experts believe BMI has important limitations, particularly for children and young people (whose body fat levels change as they grow), for athletic people (who tend to have higher levels of muscle mass) and for people from ethnic minority groups (who may develop health problems at low levels of body fat).

BMI was never intended for use in health and was developed in the 19th century using data from Europeans. Although child and ethnicity-specific adjusted BMIs and alternative height and weight ratios have been suggested, none of these have made enough progress to improve the reputation of BMI.

Several alternatives to BMI have also been suggested – such as waist-to-hip ratio (dividing waist circumference by hip circumference) or body volume index (which uses a 3D body scanner to estimate total body fat distribution).

But a recent study suggests that instead of BMI, we should use something called the Body Roundness Index (BRI) to get a more accurate picture of a person's body fat levels and predict health risk.

What is the body roundness index?

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

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

This latest study, which included 32,995 US adults between 1999 and 2018, found a link between BRI and death from any cause. Notably, they also found that those with the lowest and highest BRI scores had the highest health risks.

They also found that the BRI was better than the BMI at accurately detecting this risk. This is because the BRI takes into account fat stored around the belly, which is associated with a higher risk of health problems. This is different from the BMI, which only considers overall weight.

BRI vs BMI

Since BRI only requires a tape measure and a mathematical equation, it means it is as easy and accessible to use as BMI. But given that BRI is measured manually, it is subject to human error just as BMI is.

One study even found that eight out of ten trained health professionals showed so much human error when manually measuring the abdomen that they failed to notice an increase of 3 cm when the measurement was taken a second time. This margin of error is probably even greater for people taking their own measurements at home.

As a new metric, BRI still does not have the extensive data supporting its use that exists for BMI. This makes it hard to know how effective and reliable it is compared to these more established methods.

And like BMI, the BRI is a composite measure – meaning it combines several highly related measurements into a single index. This makes it very difficult to work out what effect different levels of body fat might have on health – and can lead to misleading interpretation of the results.

Although BRI can improve some of the shortcomings of BMI, it is not immune to misclassification. For example, people with high muscle mass may still face inaccuracies in their health risk assessments if their body fat distribution does not conform to the “typical” pattern around the belly. Research also suggests that the accuracy of BRI in predicting health risks may vary depending on a person's ethnicity, age, and gender.

The BRI certainly represents an advancement in the search for a more accurate alternative to BMI, focusing more on body shape and fat distribution rather than just body size. But it still has its limitations. Although this latest study gives us more data on the accuracy of the BRI, more research is still needed before we can be sure that it is better than BMI and should replace it.

Perhaps an even better way to get a picture of a person's health is to use 3D body surface imaging. This creates a scaled digital 3D image of the human body that allows health professionals to explore all possible existing body measurements, including both BRI and BMI, as well as allowing us to explore new digital options.

But no matter what measurements you or your doctor take to assess your health, it's important to remember that each individual is unique, and our bodies do — and should — always come in different shapes and sizes.

Alice Bullas is a Senior Research Fellow in the Sports Engineering Research Group at Sheffield Hallam University. This article is republished from Conversation,

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