If you’ve ever wondered, even briefly, whether you have obesity, you might want to double-check right about now. New research suggests that over two-thirds of Americans are considered obese under criteria released this year—well above the obesity rate based on the older standard.
Researchers at Mass General Brigham examined health records from a large, diverse sample of Americans. They found that nearly 70% of people met the new criteria for obesity, which takes into account other measurements besides body mass index. Those only classified as obese under this new definition still had a higher overall risk of health problems than nonobese people, suggesting the expanded criteria can help doctors better catch these issues before they worsen, the researchers say.
“Our findings suggest that the new obesity definition effectively stratified individuals at high-risk of organ dysfunction and long-term complications,” the authors wrote in their paper, published Wednesday in JAMA Network Open.
Beyond BMI
In January 2025, a large group of obesity experts around the world backed by the Lancet pushed for a dramatic change in how doctors diagnose the condition. It was the culmination of a long-running movement by some doctors and patients to think beyond BMI. Their newly devised criteria, published in a report that same month, was endorsed by many health- and obesity-related organizations, including the American Heart Association in the U.S.
BMI is calculated using a person’s weight and height. And traditionally, obesity is defined as having a BMI of 30 and over. The updated definition doesn’t entirely abandon BMI but rather calls for doctors to use other bodily measurements, either alongside BMI or in place of it. These other measurements are waist circumference, waist-to-hip ratio, waist-to-height ratio, and the DEXA scan (a test that directly measures a person’s bone density and body fat).
The criteria authors argued that their new definition makes it easier for doctors to determine when someone has excess body fat, one of the main reasons why obesity can negatively affect health. They also stated their criteria can better capture cases of clinical obesity—obesity especially likely to be harmful and raise the risk of other serious health problems—than the old BMI-only system. But the researchers say theirs is the first study to comprehensively examine the implications of applying this criteria in the real world.
Hidden obesity
The researchers examined data from the All of Us program, a long-running federal initiative to collect detailed health information from a diverse group of Americans. All told, they looked at the long-term health outcomes of over 300,000 American adults.
Under the old criteria, 42.9% of people in the sample were considered obese, a percentage in line with the national obesity rate tracked by the Centers for Disease Control and Prevention (a smidge over 40%). But under the new criteria, the percentage of obese people rose to 68.6%, including 36.1% who were considered clinically obese.
Nearly all the people who met the old standard of obesity continued to be included under the new framework of using BMI plus another measurement. And just about all the extra new cases of obesity involved people who appeared to have “normal” BMI but had elevated levels of the other measurements. Importantly, people with less stereotypical obesity were still more likely to have organ dysfunction and a later risk of diabetes than people not classified as obese under the new definition. That said, people with classic obesity still seemed to have a higher risk of these health problems than people with obesity who had a normal BMI.
The results indicate that this new criteria isn’t excluding people who would have been diagnosed obese in the past—a finding supported by other recent research. Moreover, it should help doctors identify people with hidden excess body fat and obesity, the researchers say. Ideally, this earlier detection can then help doctors prevent or better manage people’s obesity-related complications like diabetes.
“Identifying excess body fat is very important as we’re finding that even people with a normal BMI but with abdominal fat accumulation are at increased health risk,” said co-lead author Lindsay Fourman, an endocrinologist at MGB’s Department of Medicine, in a statement from the hospital. “Body composition matters—it’s not just pounds on a scale.”
If widely adopted, this new system could pose some unique wrinkles of its own, though. The authors note that about a quarter of people with clinical obesity in the study wouldn’t be eligible for newer obesity medications like GLP-1 therapy, for instance. And while clinical trials have found that these drugs are substantially effective for people with classical obesity, it’s an open question as to how beneficial they would be for people who don’t fit the traditional standard of obesity.
“Thus, implementation of the new framework may have significant ramifications for patients, including existing GLP1RA users, and creates a compelling need to evaluate use of antiobesity medications within this redefined target population,” the authors wrote.
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