For years, body mass index has been the standard way to measure body fat and, by extension, assess health risk.
But BMI—a calculation based on height and weight—has been widely criticized as flawed and misleading, and some health professionals have stressed the importance of developing other ways to monitor obesity and health.
Enter the body roundness index, or BRI, a new medical screening tool that considers height and waist circumference—but not weight. A recent study published in JAMA Network Open found that BRI may be a more accurate way to estimate obesity than BMI, sparking attention online about this potential BMI alternative.
So how exactly does the body roundness index work? And what do doctors think about it? Here’s what you need to know.
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BRI is what it sounds like: a measure designed to capture a person’s “roundness.”
According to Ali Rezaie, MD, a gastroenterologist and associate clinical professor at the University of California, Los Angeles, BRI involves a complicated formula (which you can find for free online) using a person’s height, waist, and hip measurements.
“How round the body is directly correlates with body fat distribution, especially abdominal fat, [or] ‘central obesity,’” he told Health. “Abdominal fat is a strong predictor of cardiac disease, diabetes, and even risk of death.”
The BRI scale ranges from one to 16, with higher scores indicating a more round body shape, Britta Reierson, MD, a family physician and obesity medicine specialist at Knownwell, told Health.
The formula was developed by Diana Thomas, PhD, a professor of mathematics at West Point, and first introduced into the scientific literature in a 2013 study in the journal Obesity.
The body mass index uses height and weight to categorize people as underweight, normal, overweight, or obese. From there, healthcare providers may use your BMI to help determine whether your weight puts you at risk for certain health conditions.
But this system has long been criticized as flawed because it doesn’t factor in variables such as sex, race, age, and ethnicity.
The metric is ”based primarily on data collected from previous generations of non-Hispanic white populations,” according to a 2023 statement by the American Medical Association warning that BMI is “an imperfect way to measure body fat in multiple groups.”
BMI also doesn’t differentiate between fat and muscle or account for fat distribution, said Luke Twelves, MD, a general practitioner and vice president of medical at Lindus Health. “As a result, BMI can misclassify people, labeling muscular individuals as overweight or obese, while failing to identify individuals with normal weight but high abdominal fat as being at risk,” he told Health.
Research on BRI shows that it holds promise as a more accurate predictor of body composition and health risks.
BRI can “accommodate variations in body composition and fat distribution across gender and different ethnicities in comparison to BMI,” Reierson said. “By including the waist and hip measurements, the BRI offers a more comprehensive evaluation of body shape and distribution of body fat.”
In the study published this June, researchers found a correlation between people with a higher BRI and an increased risk of death from any cause.
Interestingly, people with lower scores, particularly those aged 65 and older, also had a significantly increased risk of death of any cause. This finding potentially indicates “that a low BRI is suggestive of malnutrition, fatigue, reduced activity tolerance, and muscle atrophy—all indicators of a less healthy status and, consequently, lower health,” Michael Snyder, MD, the medical director of the bariatric surgery center at Rose Medical Center in Denver, told Health.
In her 2013 study, Thomas and her colleagues found that BRI predicts amounts of visceral tissue, or fat around the abdomen, better than BMI. A meta-analysis from 2020 also showed that BRI outperformed BMI (as well as other measurements) at estimating the risk for various diseases, including metabolic syndrome and colorectal cancer.
In 2021, a study found that BRI correlated strongly with insulin resistance and metabolic syndrome—both of which are precursors to diabetes and cardiovascular disease. “These findings support BRI’s potential as a superior alternative to BMI in predicting health risks associated with obesity, particularly abdominal obesity,” Twelves said.
While BRI is a promising metric, it’s not without limitations.
“One drawback is that it may still not fully capture the complexity of body composition across all populations,” Areces told Health. “More research is needed to validate BRI across different ethnic groups, ages, and genders to ensure its broad applicability.”
The BRI calculation may also be more prone to error because it’s more difficult to take accurate waist measurements, Naomi Parrella, MD, a physician specializing in obesity medicine and the chief of lifestyle medicine at Rush University Medical Center, told Health. “For example, if two people measure someone’s waist, they might have the measuring tape at slightly different places, and the person may puff out or suck in their stomach just a bit differently each time, both resulting in different measurements,” she said.
Rezaie had similar concerns. “Variations in measurement techniques can impact accuracy and reproducibility,” he said.
Plus, unlike the relatively straightforward cut-offs for BMI, BRI values aren’t as easy to interpret and may be harder to implement in routine practice, Rezaie explained. “BRI is still relatively a new measure and has not been studied as extensively as BMI, which has been around for more than a hundred years,” he said.
Meanwhile, Reierson was hesitant about the terminology. “I am not in favor of the term ‘round’ in the Body Roundness Index as I worry it is a stigmatizing and potentially triggering term,” she said. “Through conversation and education, we can likely overcome this barrier, but it has given me pause.”
