Why ‘body roundness index’ could be the new BMI, and what it says about your health

For years, we’ve been told that BMI is the final word on whether or not someone can be deemed a healthy weight for their height. But no longer, according to worldwide research published in the Lancet last night. The Commission, which was endorsed by over 75 medical organisations around the world, determined that doctors have been “overdiagnosing” people as obese and missing those of us who really do have dangerously high levels of fat.

“People with excess body fat do not always have a BMI that indicates they are living with obesity, meaning their health problems can go unnoticed,” said commissioner Professor Robert Eckel, from the University of Colorado Anschutz Medical Campus. Others meanwhile “have a high BMI and high body fat but maintain normal organ and body functions, with no signs or symptoms of ongoing illness”.

In other words, you can be slim while carrying a dangerous amount of fat around your waist, or between your organs – while a much larger person who carries their fat in their arms and legs could be deemed healthy. There is a mountain of evidence to the point. Research published last year found that in 10,000 people in China, those with the “roundest” body types – or the largest waist-to-height ratio – could be up to 163 per cent more likely to develop heart disease than those who carried their fat elsewhere.

The latest thinking is that quantifying the healthiness of our waistlines with a new “body roundness index” (BRI) might be a favourable way of determining our risk of heart disease and early death. While BMI measures weight in proportion to height to determine whether you’re overweight, BRI “converts your waist and height measurements into a shape estimation based on how circular or elliptical a person is in a general sense,” says Brendon Noble, a professor in regenerative medicine and the head of life sciences at Westminster University.

The authors of the worldwide Commission suggested that instead of BMI alone, doctors could use waist-to-height ratio to determine a patient’s health, a measure that the NHS added to its own BMI calculator tool last autumn. Doing so makes sense, Prof Noble says, because while fat clustered around your abdomen and vital organs has been shown to be a health risk in countless studies, “subcutaneous” fat in other areas is not linked to worse health outcomes.

Here’s what you need to know about BRI and why experts are favouring this new measurement over BMI.

What is BRI?

BRI compares your waistline to your height, giving a score somewhere between one and 20 (similar to BMI, which also provides a score). But it also includes “complicated equations added in to try and make that score more meaningful,” says Prof Noble.

Invented by American researchers in 2013, BRI was developed as a more accurate measure because BMI doesn’t differentiate between muscle and fat. It means that “someone with a lot of muscle could end up with a BMI that puts them in the overweight category”, Prof Noble says. Instead, BRI is likely to indicate how much extra weight you’re carrying around your middle.

What is a healthy BRI?

A “healthy” BRI score is under three, but above 0.3. Confusingly, it’s possible to be healthy according to your BRI but overweight according to BMI, and vice versa. A “healthy” BMI is regarded as being a number anywhere between 18.5 and 25.

Based on the average body sizes of men and women in Britain, both have an average BRI of 3.8. The average BMI for both men and women in the UK hovers around 27, making us too round and overweight as a nation by both measures.

What does your BRI mean for your health?

While BMI looks at your height and weight, BRI specifically looks at waist circumference and some scientists believe that it is a better indicator of many health problems, such as kidney disease, cancer, heart disease and early death in general. “Lots of studies suggest that the more body fat you have, the more prone to these you are,” says Prof Noble.

BRI is a good indicator of your body fat percentage. It measures your waist circumference in relation to your height and can tell you how much fat you have compared to your muscle mass.

The important thing here is your visceral fat, the sort found deep inside our abdomens and between our organs. While BRI doesn’t directly measure the amount of visceral fat on your body, “typically the amount of visceral fat you have is a fixed percentage of your overall body fat”, Prof Noble says – around ten percent of the total body fat you carry.

“We’ve still got plenty to learn about fat and how it can impact our health,” Prof Noble says, “but visceral does appear to be more dangerous than subcutaneous fat, based on the research.”

People with large amounts of visceral fat are more likely to have a stroke and at an earlier age, some studies have found, with this type of fat also linked to cancer, Type 2 diabetes and heart disease.

Researchers studying BRI directly, without considering visceral fat in particular, have seen similar results over the last decade, too. One study released last year found that a high BRI is a risk factor for colorectal cancer in particular, while another in 2021 found that BRI is a good predictor of which patients who have hypertension will also develop diabetes.

Other long-term studies have found that a high BRI leads to a higher risk of death in general, and especially death from heart disease.

How does BRI compare to BMI?

As a measure of risk from cardiometabolic disease, kidney disease and cancer, the very first study examining body roundness and body fat distribution found BRI to be a significantly more accurate predictor than BMI.

BMI as a measure might be more crude. In one study last year, results showed no significant increase in the risk of death for those 65 years and older with BMIs between 22.5 and 34.9. This does not seem true of people classed as obese, however: another study has found that having a BMI over 30 almost quadruples death risk.

Both measures are useful, Prof Noble says, “in that it reminds us that being overweight is bad for our health”.

“It’s also helpful that people can measure their waists and understand the change in them, as that’s often a good reflection of their overall health and any lifestyle changes they might have made without noticing.”

How can you improve your BRI?

It’s a well-known maxim that you can’t spot-burn fat. But as Prof Noble says, “it’s all very well knowing whether your BRI is high, but the important thing is what you can do about it”.

A stint on the treadmill won’t necessarily burn your belly fat on its own, “since it has been shown that, for some, exercise increases appetite and offsets the benefit,” but “we know that putting on muscle is great for reducing visceral fat”.

Over a long stretch of time, strength training might be an especially good way to reduce your BRI (or keep your waistline from expanding).

One Harvard study from 2014 found that weightlifting is the single best way to prevent a gain in waist circumference in men, even when performed for just 20 minutes per day.

But changing your body composition “doesn’t require anything crazy,” Prof Noble says. “For most people it’s just a matter of knowing that you’ve let go of control a bit too much, and reigning things in through a healthier diet and a bit more exercise.”