More Americans may be classified as obese under new definition, study suggests

New criteria for obesity are putting more Americans into that category.

Researchers at Mass General Brigham have proposed a major update to how obesity is defined, which would classify nearly 70% of U.S. adults as obese, according to a new study published in JAMA Network Open.

The new benchmark adds waist and body fat measurements to BMI, revealing body fat locations instead of just overall body weight.

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With these new criteria, the estimated obesity rate in the U.S. increases from 42.9% to almost 70%, after examining 300,000 people.

This captures an array of individuals who may have previously been considered healthy, but actually face a higher risk of conditions like heart disease and diabetes.

The increase was highest among older adults, as nearly 80% of participants over 70 years old met the obesity mark, the researchers noted.

The study highlights the limitations of a BMI-based approach, which does not consider how fat stored throughout the body can predict overall health.

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Co-first author Lindsay Fourman, M.D., an endocrinologist in the endocrinology division of the Mass General Brigham Department of Medicine, reacted to these findings in a statement.

"We already thought we had an obesity epidemic, but this is astounding," she said. "With potentially 70% of the adult population now considered to have excess fat, we need to better understand what treatment approaches to prioritize."

Abdominal fat accumulation, known as visceral fat, has "long been recognized as metabolically harmful," according to Philip Rabito, M.D., a specialist in endocrinology, weight loss and wellness in New York City.

It is also linked to an increased risk of conditions like diabetes, dyslipidemia, hypertension and cardiovascular disease, he told Fox News Digital.

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Redefining obesity to include patients with high-risk fat distribution could help "direct greater clinical attention and resources" to this "vulnerable" group, Rabito suggested.

"In addition, more of these patients may become eligible for GLP‑1-based therapies than under prior definitions, with the potential to meaningfully reduce their future cardiovascular risk," he added.

Dr. Mary Claire Haver, board-certified OBGYN and founder of The 'Pause Life, also said she was not surprised by the study findings.

"I have been watching this trend unfold in my clinic for years," the Texas-based doctor told Fox News Digital. "What concerns me most is that headlines like this often rely almost exclusively on weight-based measures such as BMI, which are blunt tools and miss what actually drives long-term health risk."

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She added, "From a physiologic and metabolic standpoint, fat distribution matters far more than body weight alone."

Haver reiterated that visceral fat, stored deep in the abdominal organs, is the "primary driver" of insulin resistance, cardiovascular disease, fatty liver disease and inflammatory risk. Fat that is visible on the surface, called subcutaneous fat, does not carry the same metabolic risk when paired with "adequate muscle mass."

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"In my patient population, I routinely see individuals who technically meet criteria for obesity based on BMI, but have high lean muscle mass, relatively low visceral fat and excellent metabolic health," she said.

"This group represents roughly 20% of patients labeled as obese in my practice, and they require very different counseling and nutrition recommendations than patients with significant visceral adiposity."

Focusing only on weight can obscure who is "truly at risk," Haver warned, and contributes to stigma while distracting from the "real issue" of metabolic health.

"Tools that assess body composition, waist circumference and markers of insulin resistance give us a far more accurate picture than the scale ever could," she said.

The doctor projected that obesity population numbers will likely improve with the expansion of GLP-1 medications.

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"But if we do not shift the conversation away from weight alone and toward body composition and fat distribution, we will continue to misclassify risk and miss opportunities for more personalized, effective care," she added.