Most Americans May Now Be ‘Obese’ Without Gaining A Pound

Health statistics often feel definitive until the criteria behind them are updated. That’s exactly what’s happening with obesity rates in the United States.

The change isn’t due to sudden weight gain across the population, but because the medical definition of obesity is being reconsidered. Right now, a 2024 report from the Centers for Disease Control and Prevention shows that more than two in five U.S. adults - over 40% - are classified as obese.

However, a study published in JAMA Network Open suggests that adopting a new diagnostic model could raise that number to around 70%. That means millions of Americans could be labeled obese without their bodies changing at all. So, what’s different?

For decades, the U.S. has relied on Body Mass Index (BMI), a simple formula based on height and weight. While easy to apply on a large scale, BMI has faced criticism for treating all bodies the same and ignoring factors like fat distribution, muscle mass, and overall metabolic health.

The updated framework leans toward a broader medical definition, closer to the World Health Organization’s description of obesity as a “chronic complex disease defined by excessive fat deposits that can impair health.” This shift could dramatically reshape how obesity is diagnosed in the future.

Doctors say obesity should be defined by where fat is stored, not just weight or BMI.

Why? Because BMI doesn’t differentiate between fat and anything else. It doesn’t account for muscle mass, bone density, age, or biological sex. This means a bodybuilder with significant muscle could be labeled obese, while someone with a lower BMI but a high amount of abdominal fat, which carries serious health risks, could be classified as “healthy.”

Doctors in Massachusetts recently argued that it’s time to move past BMI as a standalone marker. As reported by The Independent, these researchers proposed expanding the definition of obesity to account for how fat is distributed across the body, rather than just how much someone weighs.

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In the new framework, BMI is still part of the equation, but it’s no longer acting alone. Other measures, such as waist circumference, waist-to-hip ratio, and waist-to-height ratio, are now included. Someone would be diagnosed with obesity if they have a high BMI and at least one elevated waist-based metric.

To test this approach, researchers analyzed data from over 300,000 patients. The outcome was eye-opening: under the revised definition, the number of adults classified as obese jumped from 40% to an estimated 70%.

That means, based on this model, roughly 7 in 10 American adults could now fall into the obesity category.

And according to the researchers, this isn’t inflating numbers; it may be revealing what’s already true. They found that individuals who were newly classified as obese under the updated criteria had higher risks of diabetes, cardiovascular disease, and even mortality compared to those not labeled obese.

Most adults are now classified as having excess fat under the new obesity definition.

Co-first author Dr. Lindsay Fourman explained the implications clearly:

“With potentially 70 percent of the adult population now considered to have excess fat, we need to better understand what treatment approaches to prioritise.”

Older adults saw the sharpest increase under the updated definition, likely because fat distribution becomes riskier with age. The findings also suggest that many people who were previously in a “gray zone” may now be eligible for earlier intervention or treatment, including access to obesity-related medications.

Senior author Dr. Steven Grinspoon emphasized why BMI alone has been insufficient:

“We have always recognised the limitations of BMI as a single marker for obesity because it doesn’t take into account body fat distribution. 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.”Unsplash

At least 76 health organizations, including the American Heart Association and The Obesity Society, have already backed the expanded definition. In short, the medical understanding of obesity is shifting toward a more nuanced view of body fat and health risks.

And if this new system becomes widely adopted, a significant portion of the population will find themselves in a different health category than they were the day before, without changing their diet, exercise routine, or body weight.