September 6, 2024
Move over, body mass index (BMI). Make room for roundness—to be precise, the body roundness index (BRI), reports The New York Times.
The body mass index is a ratio of height to weight that has long been used as a medical screening tool. It is one of the most widely used health metrics—but also one of the most reviled, because it is used to label people overweight, obese or extremely obese.
The classifications have been questioned by athletes like the American Olympic rugby player Ilona Maher, whose BMI of 30 technically puts her on the cusp of obesity. “But alas,” she said on Instagram, addressing online trolls who tried to shame her about her weight, “I’m going to the Olympics and you’re not.”
Advocates for overweight individuals and people of color note that the formula was developed nearly 200 years ago and based exclusively on data from men—most of them white—and that it was never intended for medical screening.
Even physicians have weighed in on the shortcomings of BMI. The American Medical Association warned last year that BMI is an imperfect metric that doesn’t account for racial, ethnic, age, sex and gender diversity. It can’t differentiate between individuals who carry a lot of muscle and those with fat in all the wrong places.
“Based on BMI, Arnold Schwarzenegger when he was a bodybuilder would have been categorized as obese and needing to lose weight,” said Dr. Wajahat Mehal, director of the Metabolic Health and Weight Loss Program at Yale University.
“But as soon as you measured his waist, you’d see, ‘Oh, it’s 32 inches.’”
So welcome a new metric: the body roundness index. BRI is just what it sounds like—a measure of how round or circlelike you are; using a formula that takes into account height and waist, but not weight.
A paper published in JAMA Network Open in June was the latest in a string of studies to report that BRI is a promising predictor of mortality. B.R.I. scores generally run from 1 to 15; most people rank between 1 and 10. Among a nationally representative sample of 33,000 Americans, BRI. scores rose between 1999 and 2018, the new study found.
Their overall mortality risk was almost 50% greater than those with BRIs of 4.5 to 5.5, which were in the midrange of the sample; while those with B.R.I. scores of 5.46 to 6.9 faced a risk that was 25% higher than those in the midrange.
But those who were least round were also at elevated risk of death: People with BRI scores under 3.41 also faced a mortality risk that was 25% higher than those in the midrange, the study found.
The paper’s authors suggested the lower scores—seen mostly in those 65 and older—might have reflected malnutrition, muscle atrophy, or inactivity.
“BMI cannot distinguish body fat from muscle mass,” Wenquan Niu, who works at the Center for Evidence-Based Medicine at the Capital Institute of Pediatrics in Beijing and was a senior author of the paper, wrote in an email. “For any given BMI, fat distribution, and body composition can vary dramatically.”
Indeed, Dr. Niu wrote, “When BMI is used to frame risk, it often overestimates risk for muscular athletes, whereas it underestimates risk for older persons with muscle mass that’s been replaced by fat.”
Research contact: @nytimes
