BMI v BRI: What’s the Difference?

Melbourne-based bariatric and laparoscopic surgeon Mr Jason Winnett says clinicians and patients around the world have welcomed the recent decision to redefine clinical weight loss with the new Body Roundness Index (BRI).

According to the landmark new guidelines, while the 200+-year-old Body Mass Index (BMI) remains a useful screening tool, it has now been enhanced with the addition of other measurements – such as waist circumference, waist-to-hip ratio, waist-to-height ratio, and body fat scans – for a more accurate evaluation of pre-clinical and clinical obesity.

What’s wrong with BMI?

In decades past, Body Mass Index (BMI) has been the go-to tool for doctors to gauge whether a patient is underweight, normal weight, overweight or obese. ‘Yet this tool was devised by a mathematician in the 1830s, who was not a doctor per se,’ says Mr Winnett.

‘And while the BMI may have been useful for those in charge of population-wide research, it is not always up to the task for individual doctors and patients looking to measure weight accurately.’

Mr Winnett says, ‘When explaining these changes to patients, I basically tell them that we still use the BMI, but also the BRI, which uses extra measures for individual differences.

‘I give the example of athletes who often are not overweight and may have a lot of muscle mass, which weighs more than fat. This technically puts them in an almost obese range.’

So, what is BRI?

The Body Roundness Index (BRI) is a relatively new metric designed to estimate body fat percentage and visceral fat (the fat around internal organs) by using waist circumference and height. Unlike BMI, which only factors in weight and height, BRI captures body shape and fat distribution, making it a more precise predictor of obesity-related health risks.

Even with the new guidelines, Australia’s peak body for dietetics and nutrition, Dietitians Australia, has also cautioned health professionals not to overemphasise pathologising weight metrics.

Dr Fiona Willer, president of Dietitians Australia, says, ‘While we welcome the approach to be more modern – including adding a suite of options beyond BMI – we really must be extremely cognisant of the impact of pathologising body size.

‘We know people living in larger bodies who are seeing their healthcare professionals with a health concern are at risk of having their concern ignored or incorrectly attributed to their body weight.

‘We must ensure that proper duty of care is taken in every circumstance, and this includes further investigations to identify an individual’s condition or concern – such as malnutrition and eating disorders – even when presenting in a larger body size.’1

What are the new guidelines for defining obesity?

Mr Winnett says, ‘I tell patients that if they have gained a lot of weight and have knee pain when they walk, or trouble breathing during simple activities, or have been diagnosed with high blood pressure, these are all signs that body fat is affecting their health and that this is “clinical obesity”.

‘I then explain that the milder condition is pre-clinical obesity, where the patient may have no health problems now, but, due to excess weight, is at a higher risk of developing conditions such as diabetes or heart disease in the future.’

Image source: The Lancet Diabetes and Endocrinology Commission

What’s the best way for patients to measure at home?

Waist measurement2: Measuring the waist circumference can help screen for health risks associated with obesity. To measure the waist circumference properly, patients should stand up, exhale, relax their abdomen, place the measuring tape around their waist (just above the hip bones), and note down the measurement.
Waist-to-hip ratio3: Waist-to-hip ratio is the circumference of the waist divided by the circumference of the hips. According to this Harvard article, ‘waist circumference is measured at the smallest natural waistline (usually near the belly button) and hip circumference at the widest part of the hips.’ Waist-to-hip ratio is important because hip fat is less dangerous than belly fat stored around the stomach, which increases disease risk and prevents the organs from doing their job.
Waist-to-height ratio4: This is calculated by dividing your waist circumference by your height. A healthy waist-to-height ratio is generally considered to be below .5, meaning your waist should be less than half your height.

How does this affect GPs and other health workers?

The new BRI for defining obesity offers healthcare professionals a clearer way to differentiate between patients at risk of future health issues and those already experiencing obesity-related complications.

For patients, the introduction of the BRI means a more accurate assessment of health risks and obesity-related conditions. For health professionals, it offers improved diagnostic precision, while also reinforcing the importance of addressing each patient’s health thoughtfully and without bias.

While BMI and BRI provide useful data, they don’t tell the whole story. ‘What we’re focused on is people’s improvement in their health and well-being,’ Mr Winnett says. ‘The number itself on the scales is nowhere near as important as the improvement in your health.’

Want to learn more about incorporating BRI into your practice? Reach out here or call us on (03) 9417 1555.

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