You probably know your BMI number, or at least you know it exists. For decades it has been the first thing a doctor checks when weighing up heart risk. But many people quietly suspect it misses the point about where the body actually carries the weight.
A UK Biobank study has now compared six different body measurements in 395,831 adults aged 40 to 70. One called the Body Roundness Index came out as the single best predictor of future heart attacks.
The findings were published in October 2026 in the Journal of Health, Population and Nutrition.
The researchers tracked participants for a median of 13.3 years and recorded 14,419 heart attacks. People in the top quartile of Body Roundness Index had a 52 percent higher risk than those in the bottom quartile.
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For comparison, the top BMI quartile carried a 32 percent higher risk. Waist circumference pushed it up by 40 percent, and the weight-adjusted waist index by 46 percent.
How the Body Roundness Index is calculated
The Body Roundness Index was developed in 2013 and uses only two numbers, waist circumference and height. It treats the torso roughly like an ellipse and estimates how round the body is, rather than how heavy it is.
That matters because fat around the waist, especially the deep fat around organs, is tied more directly to cardiovascular risk than overall weight.
According to the American Heart Association, the index reflects the proportion of abdominal and visceral fat, which standard BMI cannot capture on its own.
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That is also why BMI has drawn mounting criticism in recent years, and why body fat scans get it wrong for more than 1 in 3 adults when the goal is estimating true body fat.
Why the researchers urged caution anyway
Before anyone trades BMI for roundness, read the small print. The study itself called the improvement over other measures statistically significant but modest.
In the raw numbers, the gap was small. The Body Roundness Index scored 0.710 on a standard predictive accuracy scale. The other five tools scored between 0.697 and 0.708. That is a difference of hundredths, not tenths.
The authors added that whether a gap this small is big enough to make the index a routine clinical tool still needs more validation.
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What the number means for ordinary readers
A separate cohort of 32,995 US adults from the NHANES survey, published in 2024 in JAMA Network Open, looked at how the index tracks with the risk of dying from any cause.
That study found a U-shaped pattern. Adults with a Body Roundness Index of 6.9 or higher had a 49 percent higher death rate than those in the middle range. At the other end, those with an index below 3.4 had a 25 percent higher rate.
Most adults land somewhere between those two extremes. Free online calculators let anyone plug in their waist and height to work out the number before their next check-up with a doctor.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.