Nearly 7 in 10 U.S. Adults May Now Be Classified as Obese—Here's Why

A groundbreaking study reveals that nearly 70% of American adults could now be classified as having obesity under updated criteria that look beyond traditional body mass index (BMI) measurements. Researchers at Mass General Brigham found that adding waist and body fat measurements to BMI raises the estimated obesity rate from about 40% to nearly 70%, capturing people who were previously considered healthy but face higher risks of diabetes and heart disease.

What Makes This New Definition Different?

For decades, obesity has been defined primarily using BMI, a simple calculation based on height and weight. However, this approach doesn't capture how fat is distributed throughout the body, which can be crucial for health risks. The updated framework identifies obesity in two main ways that provide a more complete picture of health status.

Under the new guidelines, people can be classified as having obesity through these approaches:

• BMI-Plus-Anthropometric Obesity: Individuals with high BMI plus at least one elevated measurement like waist circumference or waist-to-height ratio
• Anthropometric-Only Obesity: People with normal BMI who have at least two elevated body measurements that indicate excess abdominal fat
• Clinical vs. Preclinical: The guidelines further separate obesity into forms with or without physical impairment or organ dysfunction

"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 Dr. Steven Grinspoon, Chief of the Metabolism Unit in the Endocrinology Division at Mass General Brigham.

How Many Americans Does This Actually Affect?

The research analyzed data from more than 300,000 Americans in the National Institutes of Health All of Us Research Program. Using the new definition, 68.6% of participants met the criteria for obesity, compared with 42.9% under the traditional BMI-based approach. The entire increase was attributed to individuals classified as having anthropometric-only obesity—people who would not have been considered obese under older standards.

Age showed the largest effect, with nearly 80% of adults over 70 meeting the new criteria. This suggests that as we age, fat distribution patterns change in ways that traditional BMI measurements might miss, potentially leaving health risks undetected.

Why Should People Care About This Change?

The study found that people with anthropometric-only obesity—who wouldn't have been labeled as having obesity under older standards—had higher rates of diabetes, cardiovascular disease, and mortality compared with individuals without obesity. This means the new definition isn't just capturing more people arbitrarily; it's identifying individuals who face real health risks that were previously overlooked.

"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," explained Dr. Lindsay Fourman, an endocrinologist in the Metabolism Unit. "Body composition matters—it's not just pounds on a scale."

Roughly half of all participants who met the new obesity definition were categorized as having clinical obesity, meaning they showed signs of physical impairment or organ dysfunction. Importantly, this percentage was only slightly lower among those with anthropometric-only obesity than among those with BMI-plus-anthropometric obesity, suggesting similar health impacts across both groups.

The new standards have already gained significant support, with endorsements from at least 76 organizations, including the American Heart Association and The Obesity Society. However, researchers note that additional studies are needed to better understand why anthropometric-only obesity develops and which treatments may be most effective for this newly defined group.