Beyond BMI: What is the body roundness index?

By now, you're probably all too familiar with the term BMI, or your body mass index. For years, it's been the main character when it comes to assessing the human body.

Underweight, "normal" weight, overweight, obese. These are the options for the BMI, based on the individual's height and weight [2].

If it sounds like that's not a lot of information to work with, given that every human body shape is different, you're correct!

But these days, people are looking for alternate ways to assess a person's weight and body composition. Enter: the body roundness index, or BRI.

In this article, we'll break down everything you need to know about exactly what the body roundness index is, what a healthy body roundness looks like, and how the BRI shapes up when compared to the body mass index we're all familiar with.

The limitations of BMI

Despite its widespread use, the body mass index (BMI) has several limitations when it comes to categorising people as underweight, normal weight, overweight or obese.

For instance, the BMI has no way to differentiate between weight from fat mass and weight from muscle mass, and it doesn't take bone density into account, either.

This can be an issue for athletes, in particular, as they often have a low body fat percentage, but a high body mass index, which can mean that they're misclassified as overweight or obese [1].

In a similar vein, the BMI doesn't take a person's fitness levels into account and may label active people who are perfectly healthy on a metabolic level as overweight or obese [1].

This approach can be counterproductive and even harmful, as it can perpetuate weight stigma and lead to oversimplified views of health.

The BMI also cannot take a person's fat distribution into account. This can be an issue because visceral fat mass (around the internal organs) is more harmful than subcutaneous fat mass (fat that sits under the skin), but the BMI treats all fat equally [1].

Finally, the body mass index also categorises people at the broadest level, which means that it ignores differences between the sexes, age-related changes, and many cultural and ethnic differences [1].

For example, men and women have naturally different body fat percentages, but the BMI uses the same formula for both genders.

Older adults — who tend to lose muscle mass and gain fat — can also be misclassified by their BMI, and different ethnic groups have varying body fat distributions and different thresholds for various health risks.

Because the BMI fails to assess critical factors like blood pressure, cholesterol levels, blood sugar levels and inflammation markers, it's not an especially useful tool when assessing for health risks [1].

What is the body roundness index (BRI)?

It's no secret that every human body shape is different and that the body mass index lacks the nuance that's necessary in order to provide an accurate estimate for health risks like coronary artery disease, diabetes mellitus, and other diseases that are often found with excess belly fat [1].

That's where the body roundness index comes in.

The Body Roundness Index (BRI) is a metric that doesn't just look at the ratio of weight to height but looks at your body shape.

Developed to address the limitations of the BMI, the body roundness index was developed to provide a more accurate picture of a person's health in relation to their weight [5].

It takes measurements from your hip circumference and other factors to determine your waist-to-height ratio, which is key to the body roundness index.

The goal of the body roundness index is to work out how much of your body weight is made up of visceral adipose tissue, which is the belly fat mass we carry around our abdomens [4].

This is because visceral adipose tissue — rather than your overall weight — is linked with a higher cardiovascular risk for heart disease and cardiovascular morbidity, as well as an increased risk for developing diabetes mellitus and metabolic syndrome [4][5].

The body roundness index aims to provide a more accurate estimate of the health risks a person may be facing.

How does BRI compare to BMI?

While the body roundness index (BRI) and body mass index (BMI) are both tools used to assess health and body weight, they differ significantly in how they are calculated, what they measure, and their usefulness for health risk assessment.

The body mass index offers a general classification of whether a person is underweight, normal weight, overweight, or obese.

Using only a person's height and weight, it's very easy to calculate, but the downside of this is that the result lacks nuance when looking to address health risks.

This is because it doesn't consider fat distribution, muscle mass, and other factors that affect a person's body shape, and has no way to differentiate between subcutaneous fat and visceral adipose tissue, which is a risk factor for conditions including cardiovascular disease, metabolic syndrome, and diabetes mellitus.

It also fails to take variations due to age, sex and ethnicity into account, which can lead to misclassifications.

On the other hand, the body roundness index uses a more complex algorithm to assess a person's body shape, based primarily on their waist-to-height ratio.

This is because assessing the amount of visceral adipose tissue (body fat carried around the abdomen) a person is carrying will provide a more accurate estimate when it comes to assessing the risk of developing conditions like metabolic syndrome, diabetes mellitus, and cardiovascular disease.

The body roundness index doesn't count all body fat as equal the way that the BMI does, and takes into account that a healthy range of visceral adipose tissue for one person may be different for another, based on a number of factors, like age, sex and ethnicity.

Ultimately, the body roundness index is a valuable tool for measuring body fat in a way that looks for visceral adipose tissue levels that sit outside the healthy range.

But while it can be a better indicator of risk for various health issues, it should still be used alongside other health indicators, like blood pressure, cholesterol and blood sugar levels.

Looking at all of these measures together will provide the most comprehensive assessment of a person's health and their risk of developing health issues in the future.

How do you calculate your BRI?

We won't sugarcoat it: calculating your body roundness index (BRI) to assess body fat isn't especially easy.

It takes your waist circumference and height measurements to work out your waist-to-height ratio and body shape, but the formula for the BRI is more complex than that of the BMI.

To assess your body shape and calculate your body roundness index, you'll need to know your waist circumference and height. When measuring your waist circumference, measure around the narrowest part of your waist, above the navel but below the ribcage.

Then, you can calculate your body roundness index with the following mathematical formula [6]:

364.2 − 365.5 × √(1 − [waist circumference in centimetres / 2π]2 / [0.5 × height in centimetres]2

While you can calculate your body roundness index manually, it's much faster (and easier), to use an online calculator like this one [7].

Just pop your measurements and other relevant information in, and it will give you an indication of whether your body fat levels are in the healthy range or not.

A lower BRI indicates that your body shape carries less abdominal fat and that your waist-to-height ratio is more likely in the healthy range.

Meanwhile, a higher BRI correlates with a higher body fat percentage when looking at your waist-to-height ratio. This may put you at risk of developing metabolic syndrome, cardiovascular disease, insulin resistance, and diabetes mellitus.

What's a healthy BRI?

Unlike the BMI, there's no universal standard for what counts as a healthy BRI.

With that being said, doctors and researchers do use an individual's body roundness index as a tool to help them assess a person's body shape, estimate body fat, and predict health issues that the person may be at risk of developing based on the amount of visceral adipose tissue they're carrying.

Usually, higher BRI values are associated with a greater risk of developing cardiovascular disease, type 2 diabetes, metabolic syndrome, and hypertension [3].

But regardless of a person's body roundness index score, it's also important to take other factors into account, like fitness levels, muscle mass, and metabolic health markers.

For the average person healthy body roundness index ranges could look like this [3]:

• BRI < 4: Often indicates underweight or very low levels of body fat.
• BRI 4–6: Generally considered a range for healthy body composition, particularly if waist circumference is proportionate to height.
• BRI > 6: Suggests increasing levels of body roundness and fat, particularly around the abdomen, which could indicate central obesity.

However, these ranges can vary based on gender, age, and ethnicity. For instance, women naturally have higher body fat percentages than men, even within a healthy range, so a slightly higher BRI may still be normal.

Additionally, body fat distribution shifts with age, which may lead to a higher body roundness index even if the person hasn't experienced significant weight gain.

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