“Astounding” – 70% of Americans Have Obesity by New, More Accurate Definition

Researchers at Mass General Brigham examined a new way to define obesity that goes beyond BMI by also considering how body fat is distributed.

Obesity rates in the United States may increase dramatically under a new definition introduced earlier this year by the Lancet Diabetes and Endocrinology Commission.

Researchers at Mass General Brigham discovered that applying the updated criteria—which expands beyond the traditional body mass index (BMI) to include measurements of body fat distribution—raised obesity prevalence from around 40 percent to approximately 70 percent among more than 300,000 participants. The increase was especially notable among older adults. The study also revealed that many of the newly classified individuals faced a greater likelihood of negative health outcomes. The findings were 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.”

Moving beyond BMI

Historically, obesity has been defined using BMI, which estimates body fat by comparing weight and height. However, other body measurements—such as waist circumference, waist-to-height ratio, and waist-to-hip ratio—provide a clearer picture of fat distribution and help differentiate between fat and muscle mass.

Under the revised framework, obesity is identified in two ways: individuals with a high BMI and at least one elevated anthropometric measurement are classified as having “BMI-plus-anthropometric obesity,” while those with a normal BMI but at least two elevated anthropometric measurements are defined as having “anthropometric-only obesity.”

The new definition also distinguishes between preclinical and clinical obesity, with the latter describing cases where excess body fat leads to physical impairment or organ dysfunction. The updated criteria have been endorsed by at least 76 organizations, including the American Heart Association and The Obesity Society.

The researchers analyzed data from the National Institutes of Health’s All of Us Research Program, which includes more than 300,000 American participants. Based on the new definition, obesity prevalence reached 68.6 percent, compared to 42.9 percent under the traditional BMI approach. The increase was entirely due to individuals who met the criteria for anthropometric-only obesity. Rates varied across demographic groups, with obesity affecting nearly 80 percent of adults over age 70.

Health risks and clinical implications

Importantly, the study found that those with anthropometric-only obesity – who would not have been classified as having obesity by the traditional definition – had a higher risk of diabetes, cardiovascular disease, and mortality than people without obesity. About half of all individuals who met the new obesity criteria had clinical obesity, and this proportion was only slightly lower in the anthropometric-only obesity group compared with the BMI-plus-anthropometric obesity group.

“We have always recognized the limitations of BMI as a single marker for obesity because it doesn’t take into account body fat distribution,” said senior author Steven Grinspoon, MD, Chief of the Metabolism Unit in the Endocrinology Division of the Mass General Brigham Department of Medicine. “Seeing an increased risk of cardiovascular disease and diabetes in this new group of people with obesity, who were not considered to have obesity before, brings up interesting questions about obesity medications and other therapeutics.”

Future research and next steps

The researchers emphasize that further studies are needed to better understand the causes of and optimal treatments for anthropometric-only obesity. The research team previously developed a therapeutic that reduces waist circumference and plans to explore the utility of different treatment strategies in this newly defined population.

“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,” Fourman said. “Body composition matters – it’s not just pounds on a scale.”

Reference: “Implications of a New Obesity Definition Among the All of Us Cohort” by Lindsay T. Fourman, Aya Awwad, Alba Gutiérrez-Sacristán, Camille A. Dash, Julia E. Johnson, Allison K. Thistle, Nikhita Chahal, Sara L. Stockman, Mabel Toribio, Chika Anekwe, Arijeet K. Gattu and Steven K. Grinspoon, 15 October 2025, JAMA Network Open.
DOI: 10.1001/jamanetworkopen.2025.37619

This work was supported by the National Institutes of Health (grants K23HD100266, 1R01AG087809, T32DK007028, K23HL147799, 1R01HL173028, and P30DK040561) as well as the American Heart Association-Harold Amos Medical Research Faculty Development Program, supported by the Robert Wood Johnson Foundation, and the Robert A. Winn Excellence in Clinical Trials Award Program from the Bristol Meyers Squibb Foundation.

Disclosure: Fourman serves as a consultant to Theratechnologies and Chiesi Farmaceutici and receives grant funding to her institution from Chiesi Farmaceutici outside of this work. Grinspoon serves as a consultant to Marathon Assets Management and Exavir Therapeutics and receives grant funding to his institution from Kowa Pharmaceuticals, Gilead Sciences, and Viiv Healthcare, unrelated to this project. For the remaining authors, no conflicts were declared.

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