New waist-focused criteria suggest more than 75% of adult Americans may meet obesity guidelines than previously thought.
Obesity has always been defined by a simple equation: height divided by weight, better known as body mass index (BMI). It is fast, cheap and familiar. However, according to a new study published in JAMA Network Open, it may also be missing the bigger picture.
Researchers found that when obesity is defined using not just BMI, but also waist-based measurements, more than 75% of US adults could meet the criteria – nearly double the current estimate of around 40%. The finding reframes obesity not as a condition affecting a minority of Americans, but as the statistical norm.
For investors, policymakers and longevity-focused companies, this matters. Definitions shape markets, reimbursement, prevention strategies and how health risks are identified years before disease sets in.
BMI was never designed to diagnose disease. It estimates body fat using height and weight, without accounting for where fat is stored. This distinction turns out to be crucial.
“BMI is the standard measure for determining criteria for obesity. It’s the most widely known metric,” said Dr Erica Spatz, a cardiologist at Yale School of Medicine and co-author of the study. But BMI alone does not capture adipose tissue; the fat that surrounds organs, influences hormones and is strongly linked to chronic disease.
This type of fat is less visible than subcutaneous fat but “is more associated with high blood pressure, diabetes and heart disease,” Spatz said.
Someone can fall into the “normal” BMI range while still carrying dangerous levels of internal fat. The study found that nearly four in 10 adults with a normal BMI had excess body fat once waist-based measures were included.
The revised framework draws from recommendations by The Lancet Diabetes & Endocrinology Commission, endorsed by more than 70 medical organizations worldwide. It combines BMI with measurements such as waist circumference, waist-to-hip ratio and waist-to-height ratio.
Using this broader lens, researchers analysed health data from more than 14,000 participants in the National Health and Nutrition Examination Survey, representing nearly 238 million US adults between 2017 and 2023. The result: 75.2% met the new obesity criteria.
Obesity rates rose sharply with age and were higher among Hispanic adults, while remaining similar between men and women. Notably, almost all adults aged 50 and older were classified as having obesity under the updated definition, prompting calls for age-specific thresholds.
Beyond numbers, the new approach aims to change how obesity is understood and treated.
The Commission proposes distinguishing between “pre-clinical” obesity and “clinical” obesity. Pre-clinical obesity refers to excess body fat without organ damage, but with a higher future risk. Clinical obesity, by contrast, means fat is already impairing organ function or daily life.
“In other words, their organs are functioning well. They have no metabolic diseases, and they have a fairly good quality of life,” said Dr Robert Kushner of Northwestern University, describing pre-clinical obesity.
Clinical obesity, he added, is when “the extra body fat is impacting the health or the quality of life of the individual.”
For longevity medicine, this distinction shifts the focus from reacting to disease toward identifying risk earlier, when intervention is less invasive and more cost-effective.
Not everyone sees the findings as a call to immediately rewrite guidelines. The study’s authors caution that broader criteria will inflate obesity estimates and that more research is needed before widespread adoption.
Still, many clinicians see the message as unavoidable.
“We do have a major problem. Obesity is by far the most significant chronic disease in human history,” said Dr Fatima Cody Stanford of Massachusetts General Hospital.
She added that the revised definition highlights how much earlier and more precisely obesity-related risks could be identified if clinicians are trained and systems are equipped to do so.
If three out of four adults are technically living with obesity, the implications extend far beyond clinical debates. Screening tools, prevention-focused services, digital health platforms, metabolic therapies and diagnostics all stand to be affected.
More importantly, the shift reframes obesity not as a personal failure measured by a scale, but as a chronic, measurable condition tied to long-term healthspan. For a longevity economy built on early detection and personalized intervention, that change in perspective may be the most consequential outcome of all.
