New Obesity Definition Redraws U.S. Health Map: Nearly 70% of Adults Now Classified as Obese

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A Landmark Redefinition of Obesity

A major new study published in JAMA Network Open has revealed that nearly 70 percent of U.S. adults now qualify as obese under a revised definition proposed by the Lancet Diabetes and Endocrinology Commission earlier this year . The updated criteria go beyond the traditional reliance on body mass index (BMI) to include waist circumference and other measures of fat distribution—fundamentally shifting how obesity is identified and understood.

Researchers from Mass General Brigham analyzed data from more than 300,000 participants in the National Institutes of Health’s All of Us Research Program. Their findings suggest that under the new framework, obesity prevalence rises from 42.9 percent to 68.6 percent—marking one of the most dramatic reclassifications of a chronic condition in modern American health research .

“This is astounding,” said Dr. Lindsay Fourman, an endocrinologist in the Metabolism Unit of the Mass General Brigham Department of Medicine and co-first author of the study. “With potentially 70% of the adult population now considered to have excess fat, we need to better understand what treatment approaches to prioritize” .

Beyond BMI: A More Nuanced Measure

For decades, BMI—a simple calculation of weight relative to height—has served as the standard tool for diagnosing obesity. However, health experts have long criticized BMI for overlooking body composition and fat distribution. A muscular athlete and a person with high abdominal fat can share the same BMI, despite having very different health profiles.

The new definition introduces a dual model:

BMI-plus-anthropometric obesity, in which a person has both a high BMI and at least one elevated measure of fat distribution (such as waist-to-hip or waist-to-height ratio).
Anthropometric-only obesity, in which a person has a normal BMI but two or more elevated body fat distribution measures.

This more sophisticated approach acknowledges that “body composition matters—it’s not just pounds on a scale,” Dr. Fourman emphasized .

Who Is Affected Most?

The study found striking demographic differences. Under the new criteria, older adults experienced the sharpest increase in obesity rates—nearly 80 percent of Americans over age 70 now meet the definition . Women and certain ethnic groups also showed variations in obesity prevalence, reflecting differences in fat distribution patterns.

Of particular significance, individuals newly classified as having anthropometric-only obesity—those with normal BMI but higher central fat—demonstrated increased risks of diabetes, cardiovascular disease, and mortality compared with peers deemed non-obese under both definitions.

“This new group of people with obesity, who were not considered obese before, shows elevated risk for serious health outcomes,” said Dr. Steven Grinspoon, senior author and chief of the Metabolism Unit at Mass General Brigham. “That raises important questions about how obesity medications and other therapeutics should be used” .

A Shift Backed by Major Health Organizations

At least 76 organizations, including the American Heart Association and The Obesity Society, have endorsed the updated framework . Advocates argue that it more accurately captures metabolic risk and could lead to fairer access to obesity treatments, which are often rationed or restricted based on BMI alone.

However, the new criteria are not without controversy. Critics warn that redefining obesity so broadly may inadvertently medicalize normal variations in body composition, further stigmatizing individuals or overwhelming healthcare systems with newly eligible patients.

Public health experts caution that refinement in diagnosis must come hand-in-hand with nuanced messaging. “The goal isn’t to label more people as obese—it’s to better identify who is truly at risk for disease. The focus should remain on reducing metabolic harm, not on weight alone,” said Dr. Maya Thomas, a preventive medicine specialist at Johns Hopkins University (unaffiliated with the study).

Potential Implications for Care

With a majority of adults now classified as obese, U.S. health policy could face seismic adjustments. Insurance coverage for weight management programs, access to new anti-obesity medications (such as GLP-1 receptor agonists), and preventive care strategies may need to be re-evaluated.

Dr. Grinspoon’s team emphasized that treatment pathways—including lifestyle intervention, medication, or bariatric procedures—should be guided by both metabolic risk and physical impairment, not BMI alone . Their previous research has explored therapies targeting waist circumference reduction, a metric strongly correlated with cardiometabolic risk.

Limitations and Future Research

While groundbreaking, the study also carries limitations. Most notably, the All of Us cohort, though extensive, may underrepresent certain rural or lower-income populations. The observational design also prevents the establishment of direct causation between obesity classification and outcomes.

Experts agree that longitudinal studies are needed to confirm whether anthropometric-only obesity translates to higher long-term morbidity and mortality—or if targeted interventions can improve outcomes in this group.

What This Means for the Public

For individuals, the takeaway is clear: BMI alone is no longer enough to gauge health risk. Waist measurement, body fat percentage, and overall metabolic health are increasingly relevant in clinical assessment.

Dr. Thomas advises patients to interpret the new definition as an invitation to deeper self-awareness—not alarm. “Ask your doctor to go beyond BMI. Discuss waist circumference, blood glucose, blood pressure, and cholesterol. These give a much clearer picture of your health.”

Managing weight remains a multidimensional effort, encompassing nutrition, physical activity, sleep, and mental health. As science evolves, the concept of obesity may continue to shift—from a number on a chart to a profile of complex biological and behavioral factors.

Medical Disclaimer

This article is for informational purposes only and should not be considered medical advice. Always consult with qualified healthcare professionals before making any health-related decisions or changes to your treatment plan. The information presented here is based on current research and expert opinions, which may evolve as new evidence emerges.