The obesity crisis in the United States may be worse than realized. (© andriano_cz – stock.adobe.com)
7 in 10 U.S. Adults Could Fall Under New Obesity Definition
In A Nutshell
Adding waist size to BMI raises U.S. obesity rates from 42.9% to 68.6%, according to a major JAMA Network Open study.
One in four adults have “hidden” belly-fat obesity despite a normal BMI.
Older adults and Asian participants saw the biggest increase in obesity classification.
The new definition could change who qualifies for treatment and reshape healthcare policy.
BOSTON — A revolutionary change in how doctors define obesity could fundamentally reshape medical practice, according to research analyzing health data from over 300,000 Americans.
Scientists found that adopting a new obesity framework endorsed by 76 professional medical organizations increased obesity rates from 42.9% to 68.6% among study participants. This dramatic jump stems from including people who have dangerous belly fat despite maintaining what doctors previously considered a healthy weight.
Published in JAMA Network Open, the study analyzed data from the All of Us research program and represents the first large-scale examination of how new obesity guidelines would affect healthcare. The research tracked participants for four years to document real health outcomes, not just theoretical classifications.
Beyond the Scale: Why Waist Size Matters
Rather than relying solely on the height-to-weight calculation that has dominated medicine for decades, the new approach incorporates waist circumference, waist-to-hip ratio, and waist-to-height ratio alongside BMI to create a more complete health assessment.
The research team, led by endocrinologist Dr. Lindsay Fourman from Massachusetts General Hospital, found that traditional BMI measurements miss many people with dangerous fat distribution patterns. The research team found that belly fat, regardless of overall weight, serves as a key predictor of metabolic disease.
Scientists identified a category called “anthropometric-only obesity” affecting 78,047 study participants. These individuals maintain normal BMI scores while carrying elevated measurements around their midsection. Among this group, 17,426 people (22.3%) had BMI scores doctors previously labeled as normal or underweight.
BMI measurements don’t tell the whole story for some people who have higher levels of dangerous belly fat.(kwanchai.c/Shutterstock)
Health Risks That BMI Misses
Researchers tracked participants to document who developed serious health problems. People with this hidden form of obesity faced significantly higher risks than those without obesity, despite looking healthy on standard scales.
Compared to people without obesity, those with the waist-centered type were 76% more likely to have organ problems. They also faced more than double the risk of developing diabetes and 55% higher risk of heart disease.
he research team found that people with this form of obesity often developed high blood pressure, physical limitations, and sleep apnea. These conditions typically emerge gradually, making early identification through waist measurements potentially valuable for prevention.
Age and Demographics Drive Changes
The study revealed striking patterns across different groups. Among participants aged 18 to 29, obesity prevalence under the new definition reached 43.9%. The most dramatic change occurred among seniors: 78.3% of Americans over 70 in the study met criteria for obesity under the new framework, compared to previous BMI-based classifications.
This age-related increase reflects how body composition changes over time, with fat increasingly accumulating around the midsection as people get older. Among people over 70 in the study, 54.4% had what researchers called “clinical obesity” indicating the presence of organ dysfunction or physical limitations.
The research also found notable differences by race and gender. Asian participants saw the largest relative increase in obesity rates, jumping 90.3% from 2,439 participants (27.0%) to 4,641 participants (51.4%) under the new definition. Male participants were more likely than female participants to have anthropometric-only obesity, affecting 32.5% of men versus 21.7% of women in the study.
Obesity Treatment Guidelines Face Major Overhaul
The new framework could dramatically alter who receives obesity medications and treatments. Currently, 44.7% of study participants qualified for anti-obesity drugs based on BMI guidelines. Under the new framework, about half of those who currently qualify for weight-loss medication (51.2%) would be reclassified as having preclinical obesity or no obesity, suggesting they may receive lower priority for treatment.
Additionally, among participants with clinical obesity under the new definition (excluding those with diabetes already eligible for certain medications), 15,495 of 69,894 (22.2%) wouldn’t meet current eligibility criteria for recent weight-loss drug trials or FDA-approved medications. This mismatch indicates treatment guidelines may need substantial revision.
The Lancet Commission that developed the new definition recommends pharmacological treatment for all people with clinical obesity and select individuals with preclinical obesity. This represents a shift from current practice toward more targeted treatment based on health complications rather than BMI alone.
Clinical vs. Preclinical Obesity
The new approach introduces two categories. “Clinical obesity” means someone has health problems or physical limitations related to their weight. “Preclinical obesity” means early warning signs are present but serious symptoms haven’t developed yet.
About 36% of all study participants had clinical obesity, with rates climbing sharply with age. The distinction matters because people with clinical obesity faced the highest risks of future diabetes, heart disease, and death.
Even the earlier stage carried meaningful health risks. People with preclinical obesity had more than three times the risk of developing diabetes and 40% higher risk of heart problems compared to those without obesity.
The study tracked the most common health problems associated with clinical obesity: high blood pressure topped the list, followed by physical limitations and sleep apnea. The research revealed that organ dysfunction itself, even without obesity, significantly increased health risks.
For healthcare systems and insurance companies, these changes could carry massive financial consequences. Medicare and other payers may need to reassess coverage policies as the eligible population for obesity treatments potentially shifts substantially.
“We already thought we had an obesity epidemic, but this is astounding,” Dr. Fourman said in a statement. “With potentially 70 percent of the adult population now considered to have excess fat, we need to better understand what treatment approaches to prioritize.”
The study’s authors acknowledge that implementing the new definition would require more work and resources than current BMI-based screening. However, they argue that the improved ability to identify health risks may justify the additional effort, particularly if integrated into electronic health record systems.
The research’s obesity prevalence using traditional BMI-based criteria (42.9%) closely aligns with Centers for Disease Control and Prevention estimates for the US population (40.3%), supporting the potential broader applicability of these findings to American adults generally.
Disclaimer: This article summarizes recent peer-reviewed research for general information only. It is not a substitute for medical advice. Readers should consult qualified healthcare professionals for individualized assessment or treatment.
Paper Summary
Methodology
Researchers analyzed data from 301,026 adults in the All of Us research program, enrolled between May 2017 and September 2023. Participants underwent standardized measurements of height, weight, waist circumference, and hip circumference, and completed health surveys. The study used electronic health records to track health outcomes over a median follow-up period of 4 years.
Results
Under the new obesity definition, 68.6% of participants met criteria for obesity compared to 42.9% using traditional BMI-based criteria. The increase was driven by including 78,047 people with “anthropometric-only obesity” who had elevated waist measurements despite normal BMI. Clinical obesity affected 36.1% of all participants. People with anthropometric-only obesity had odds ratios of 1.76 for organ dysfunction and adjusted hazard ratios of 2.12 for diabetes and 1.55 for cardiovascular events compared to those without obesity.
Limitations
The study relied on diagnostic codes, surveys, and laboratory results to classify clinical obesity, which may not fully capture all cases of organ dysfunction. Researchers could not establish whether organ dysfunction was directly caused by obesity. The analysis used the new framework’s ability to predict future health risks as a measure of clinical utility, rather than a gold standard comparison.
Funding and Disclosures
This work was supported by grants from the National Institutes of Health, the American Heart Association, and the Bristol Myers Squibb Foundation. Lead author Dr. Fourman reported receiving grant support and personal fees from pharmaceutical companies. Dr. Grinspoon reported receiving personal fees from investment and biotech companies and grant support from pharmaceutical companies.
Publication Information
“Implications of a New Obesity Definition Among the All of Us Cohort” was published in JAMA Network Open on October 15, 2025. The study was conducted by researchers from Massachusetts General Hospital, Harvard Medical School, and other institutions.