Obesity in the United States is no longer a slow-moving crisis. A sweeping redefinition of what counts as unhealthy body fat means that nearly seven in ten adults could now fall into an obesity category, even as traditional measures suggest a lower share. The shift is forcing a reckoning with how the country measures risk, how health systems respond, and what it will take to reverse a trend that is already driving chronic disease and early death.
Instead of focusing only on weight and height, new research is centering where fat sits on the body and how it affects organs, which dramatically expands the number of people considered medically vulnerable. I see this as less a statistical quirk than a blunt message: the United States has been underestimating the scale of its obesity problem, and the margin of error is now closing.
From 40% to nearly 70%: how a definition changed the map
For years, the standard picture of American obesity came from body mass index, which compares weight to height and labels anyone with a BMI of 30 or higher as obese. Using that familiar yardstick, national survey data put adult obesity prevalence at about 40.3%, with severe obesity at 9.4%, and other analyses have echoed that 40.3% figure, noting similar rates among women at 41.3% and men. Those numbers were already alarming, given that the CDC describes obesity as a disease linked to diabetes, heart disease and other serious conditions.
New research has effectively redrawn that map. A large analysis tied to National Institutes of Health All of Us Research Program data, involving more than 300 thousand participants, applied a broader definition that combines BMI with waist measurements and other anthropometric markers. That work, highlighted in a major update to how obesity is defined, suggests that nearly 70% of U.S. adults could now be classified as obese, a finding echoed by a Harvard Study Classifies analysis that also concluded 70% of U.S. Adults may be Obese Under New Definition.
Why waistlines matter more than the scale alone
The core of this shift is a simple but powerful idea: where fat is stored can matter as much as how much there is. For decades, BMI treated a muscular athlete and a sedentary office worker with the same height and weight as identical, even though their health risks are very different. The new criteria, described in detail by Research that emphasizes why waist fat matters, focus on abdominal and visceral fat that wraps around organs and drives inflammation, insulin resistance and cardiovascular strain.
By incorporating waist circumference and related measures into the definition, the new framework captures people whose BMI might look “overweight” rather than obese but whose central fat puts them at high risk of disease. The Study Data Show a Sharp increase in risk when fat is concentrated around the midsection, and the updated criteria reflect that reality. In practice, this means that someone with a modest BMI but a large waistline may now be counted in the obesity category, while a person with a higher BMI but low visceral fat might be assessed differently, a nuance that older definitions largely ignored.
The new numbers: 70%, 70 percent, and even 75%
Once waist and body composition are factored in, the statistics escalate quickly. The Mass General Brigham team behind the redefinition reported that Nearly 70% of U.S. adults could now be classified as obese, with the effect especially pronounced among older adults. A separate analysis highlighted in a national broadcast segment noted that nearly 70% of U.S. adults are obese based on a new definition that looks at more than just BMI, reinforcing how consistent that threshold has become across different research groups.
Other work pushes the estimate even higher. A research letter summarized in a medical news briefing reported that More than three in four adults may meet criteria for obesity under the new definition, and a separate report framed it as 75% of US adults potentially qualifying. Another analysis, summarized under the headline that Studies warn nearly 70 percent of US Adults are at risk, underscores that even when researchers use slightly different thresholds, they converge on a picture in which a clear majority of adults are living with obesity-level risk.
What official surveys and state reports still show
Even as these new definitions gain traction, the older BMI-based statistics still shape policy and public perception. Federal health surveys from the National Health and Nutrition Examination Survey, summarized in a What was the prevalence of obesity in adults during August 2021 to August 2023, show obesity rates varying by age, with higher prevalence in middle age and among those 60 and older. A separate data brief confirms that obesity remained widespread in both men and women, even before the new criteria were applied.
At the state level, the picture is similarly sobering. A national “State of Obesity” assessment notes that more than 35% of adults are obese in a large share of states, while a companion Resources package of State Fact Sheets Media Briefing materials from Washington describes obesity as a driver of chronic diseases like diabetes and heart disease. Another analysis of state trends reported that obesity remains high in the US but more states are showing progress, with a Health and Human Services Department spokesman saying the administration is encouraged by the number of states where adult obesity rates have stopped rising or begun to fall.
Is obesity really “declining” or just being reclassified?
One of the more confusing aspects of the current moment is that some surveys suggest obesity is easing slightly at the same time that new definitions are expanding the count. A national poll of self-reported weight found that the share of adults who describe themselves as obese peaked at 39.9% in 2022 and has since edged down, a trend summarized under the banner of Obesity Rate Declining. That poll, conducted from WASHINGTON, D.C., also noted that fewer adults report being told by a doctor that they have diabetes, suggesting some modest improvements in metabolic health.
Set against that, however, are the more expansive clinical definitions that push the estimated prevalence to 70% or even 75%. In my view, the apparent contradiction is more about measurement than reality: self-reported surveys capture how people see themselves, while the new clinical criteria capture how their bodies actually distribute fat and respond to it. It is entirely possible for self-reported obesity to dip slightly while the underlying physiological risk remains high or even grows, especially as the population ages and more people move into higher risk categories identified by the updated definitions.
Global pressure and the King’s College London framework
The United States is not redefining obesity in isolation. Earlier in the year, a commission led by King’s College London outlined a new weight-class framework that includes more nuanced categories of risk and body composition. That framework, described in a report noting that 70% of US May Be Classed as Obese Under New Measures, reflects a broader international push to move beyond BMI as a blunt tool and toward definitions that better predict disease.
In practice, this global work is feeding directly into American debates. The Mass General Brigham analysis, the Harvard Study Classifies findings and the JAMA Network Open research letter all echo the same logic that At the start of the year, a commission led by King’s College London advanced: obesity should be defined by a combination of weight, fat distribution and metabolic markers, not by BMI alone. As U.S. clinicians and policymakers absorb that message, I expect the tension between older and newer metrics to intensify, particularly as insurers, employers and public programs decide which definition to use when designing benefits and interventions.
Who is most affected when the bar moves
When definitions change, the impact is not evenly distributed. The updated criteria appear to hit older adults hardest, with the Mass General Brigham team reporting that the jump in obesity classification is especially pronounced among older adults, and the Research on waist fat notes that those over 70 are most affected. That makes intuitive sense: as people age, they tend to lose muscle and gain central fat, which may not dramatically change BMI but does sharply increase metabolic risk.
Socioeconomic and geographic patterns also matter. The Full Report Press Release Comunicado de Prensa State materials on obesity emphasize that states with higher poverty rates and less access to healthy food and safe places to exercise often have higher obesity prevalence. When the definition broadens, those communities may see an even larger share of residents classified as obese, which could either spur more investment in prevention or, if mishandled, deepen stigma and strain already stretched health systems.
Policy, politics and what comes next
Redefining obesity at this scale is not just a medical decision, it is a political and economic one. The 2025 FACT SHEET — OBESITY IN AMERICA underscores that obesity is THE DISEASE that drives enormous health care costs, and labeling up to 75% of adults as obese under a new definition could reshape everything from insurance coverage for weight-loss drugs to workplace wellness programs. A national report framed as the State of Obesity Report 2025 from Washington argues for better policies for a healthier future, and its Resources section calls for coordinated action across federal, state and local levels.
At the same time, there is a risk that expanding the label without expanding support will simply medicalize a larger share of the population without giving them tools to change. In my view, the most constructive path is to treat the new numbers as a wake-up call rather than a verdict. If nearly 70% of adults are now considered obese by clinical standards, then the response has to move beyond individual willpower to include food policy, urban design, education and access to care. Otherwise, the country will simply be relabeling risk while the underlying epidemic continues to grow.
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