Nearly 70% of U.S. adults could now be classified as obese
A major update to how obesity is defined could push U.S. obesity rates to nearly 70%, according to a large new study. The change comes from adding waist and body fat measurements to BMI, capturing people who were previously considered healthy. Many of these newly included individuals face higher risks of diabetes and heart disease. The findings suggest that where fat is stored may be just as important as overall weight.
A newly proposed definition of obesity could significantly increase the number of Americans considered to have the condition. According to researchers at Mass General Brigham, applying updated criteria developed earlier this year by the Lancet Diabetes and Endocrinology Commission raises the estimated obesity rate in the United States from about 40 percent to nearly 70 percent. The study examined data from more than 300,000 people and found that the increase was especially pronounced among older adults. The findings also showed that many individuals newly classified under the updated definition face higher risks of serious health problems. The study was published in JAMA Network Open.
"We already thought we had an obesity epidemic, but this is astounding," said co-first author Lindsay Fourman, MD, an endocrinologist in the Metabolism Unit in the Endocrinology Division of the Mass General Brigham Department of Medicine. "With potentially 70 percent of the adult population now considered to have excess fat, we need to better understand what treatment approaches to prioritize."
Why BMI Alone May Miss Health Risks
For decades, obesity has primarily been defined using body mass index (BMI), a calculation based on height and weight. While BMI offers a simple estimate, it does not capture how fat is distributed throughout the body. Other anthropomorphic measures -- including waist circumference, waist-to-height ratio, and waist-to-hip ratio -- can provide additional insight by distinguishing fat mass from muscle and identifying abdominal fat linked to disease risk.
Under the updated framework, obesity is identified in two main ways. Individuals with a high BMI plus at least one elevated anthropometric measure are classified as having obesity, a category the authors call "BMI-plus-anthropometric obesity." People with a normal BMI can also be classified as having obesity if they have at least two elevated anthropometric measures, referred to as "anthropometric-only obesity." The guidelines further separate obesity into preclinical and clinical forms, with clinical obesity defined by obesity-related physical impairment or organ dysfunction. The new standards have already been endorsed by at least 76 organizations, including the American Heart Association and The Obesity Society.
Study Data Show a Sharp Rise in Obesity Rates
Researchers analyzed participants from the National Institutes of Health All of Us Research Program, which includes more than 300,000 Americans. Using the new definition, 68.6 percent of participants met the criteria for obesity, compared with 42.9 percent under the traditional BMI-based approach. The entire increase was attributed to individuals classified as having anthropometric-only obesity. Obesity rates differed across sex and race, but age showed the largest effect, with nearly 80 percent of adults over 70 meeting the new criteria.