The prevalence of obesity in the United States could see a significant rise under a new definition released by the Lancet Diabetes and Endocrinology Commission. Researchers from Mass General Brigham have found that by applying these new criteria, which expand beyond the traditional use of body mass index (BMI) to include measures of body fat distribution, the prevalence of obesity increased from approximately 40 percent to about 70 percent among over 300,000 individuals studied. This increase was particularly pronounced among older adults. The findings, published in JAMA Network Open, also highlight that these newly categorized individuals face a higher risk of adverse health outcomes.
“We already thought we had an obesity epidemic, but this is astounding,” stated co-first author Lindsay Fourman, MD, an endocrinologist in the Metabolism Unit of the Endocrinology Division at Mass General Brigham. “With potentially 70 percent of the adult population now considered to have excess fat, we need to better understand what treatment approaches to prioritize.”
Redefining Obesity: Beyond BMI
Traditionally, obesity has been defined by BMI, which estimates body fat based on a person’s weight and height. However, other anthropometric measures—such as waist circumference, waist-to-height ratio, or waist-to-hip ratio—can further account for fat distribution and help differentiate between muscle and fat mass.
Under the new framework, a person is classified as having obesity if they have a high BMI plus at least one elevated anthropometric measure (termed “BMI-plus-anthropometric obesity”), or if they have a normal BMI and at least two elevated anthropometric measures (termed “anthropometric-only obesity”). The new definition also distinguishes between preclinical and clinical obesity, with clinical obesity defined as the presence of obesity-related physical impairment or organ dysfunction. At least 76 organizations, including the American Heart Association and The Obesity Society, have endorsed the new guidelines.
Impact on Health Outcomes
The study analyzed participants from the National Institutes of Health’s All of Us Research Program, encompassing over 300,000 Americans. Obesity prevalence was found to be 68.6 percent with the new definition, compared to 42.9 percent under the traditional BMI-based definition. This increase was entirely driven by the inclusion of individuals with anthropometric-only obesity. Obesity rates varied by sex, race, and especially by age, affecting nearly 80 percent of adults over 70.
“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 Lindsay Fourman, MD.
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.
Expert Opinions and Future Directions
“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 at Mass General Brigham. “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.”
The researchers emphasize the need for further studies 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.
Research Authorship and Funding
The study was authored by Lindsay Fourman, Steven Grinspoon, and colleagues from Mass General Brigham, including Aya Awwad, Camille A. Dash, Julia E. Johnson, Allison K. Thistle, Nikhita Chahal, Sara L. Stockman, Mabel Toribio, Chika Anekwe, and Arijeet K. Gattu. Additional authors include Alba Gutiérrez-Sacristán.
This research was supported by the National Institutes of Health and several other organizations, with no involvement from the funding bodies in the study’s design or execution. The paper cited is “Implications of the Lancet Commission Obesity Definition Among the All of Us Cohort” by Fourman LT et al., published in JAMA Network Open.
The implications of these findings are profound, suggesting a need for a reevaluation of how obesity is diagnosed and treated in the United States. As the medical community adjusts to these new guidelines, the focus will likely shift towards developing more comprehensive treatment strategies that address the complexities of body fat distribution and its impact on health.
