Observational study indicates obesity classification in U.S. adults approaches 70% — Evidence Review
Published in JAMA Network Open, by researchers from Mass General Brigham
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Table of Contents
A new study finds that updating the definition of obesity to include additional body fat measures—beyond BMI—raises U.S. adult obesity estimates from about 40% to nearly 70%. Related research generally supports concerns about underestimating obesity and its health impacts when using BMI alone, and highlights the growing public health challenge.
- Several related studies have documented persistent increases in obesity rates in the United States based on BMI, with projections suggesting further rises; the new definition could accelerate or clarify these trends by capturing more at-risk individuals who may have been overlooked by BMI-only criteria 1 2 3 4.
- Research indicates that BMI alone fails to account for body fat distribution, especially abdominal fat, which is more closely linked to metabolic and cardiovascular risks—a limitation addressed by the updated criteria 7 12 13 14.
- Studies that examine obesity-related health outcomes consistently link excess body fat, regardless of BMI, to increased risks of diabetes, cardiovascular disease, and mortality, supporting the new study’s findings of elevated health risks among those newly classified as obese 6 8 9 10.
Study Overview and Key Findings
The recent study by Mass General Brigham, published in JAMA Network Open, addresses growing recognition that traditional BMI-based definitions of obesity may miss individuals at heightened health risk due to excess body fat in specific locations, such as the abdomen. Amid rising obesity rates and evolving clinical guidelines, the research leverages a large, diverse U.S. cohort to analyze the impact of an expanded obesity definition that incorporates both BMI and additional anthropometric measures (e.g., waist circumference). The study also explores demographic variations and associated health risks within the newly classified population—providing timely insights as policymakers and health organizations reconsider how obesity is defined and managed.
| Property | Value |
|---|---|
| Organization | Mass General Brigham |
| Journal Name | JAMA Network Open |
| Authors | Lindsay Fourman, Steven Grinspoon, Aya Awwad, Camille A. Dash, Julia E. Johnson, Allison K. Thistle, Nikhita Chahal, Sara L. Stockman, Mabel Toribio, Chika Anekwe, Arijeet K. Gattu, Alba Gutiérrez-Sacristán |
| Population | Adults in the United States |
| Sample Size | more than 300,000 people |
| Methods | Observational Study |
| Outcome | Obesity classification, health risks associated with obesity |
| Results | Obesity rate increased from 40% to nearly 70% under new criteria. |
Literature Review: Related Studies
To understand the context and implications of these findings, we searched the Consensus paper database, which includes over 200 million research papers. The following search queries were used to identify relevant literature:
- obesity rate increase United States
- health impacts of obesity
- obesity classification criteria changes
Related Studies Table
| Topic | Key Findings |
|---|---|
| How have obesity rates changed in the U.S., and what factors drive increases? | - U.S. adult obesity rates have more than doubled since the 1960s, with projections exceeding 50% by 2030; increases are especially rapid among older adults and certain demographic groups 1 2 3 4 5. - Obesity trends are influenced by age, gender, ethnicity, and socioeconomic status 1 3. |
| What are the health consequences of obesity, especially regarding fat distribution? | - Obesity, particularly abdominal/visceral fat, is strongly linked to increased risks for diabetes, cardiovascular disease, certain cancers, and mortality 6 7 8 9 10 13 14. - Health risks are not fully captured by BMI alone; body fat distribution, such as waist circumference, is a critical factor 7 8 12 13 14. |
| How do changes in obesity definitions or classification criteria affect prevalence and diagnosis? | - Shifting from BMI-only to composite or fat-distribution-based criteria identifies more individuals at risk and raises measured prevalence rates 11 12 13 14 15. - Newer definitions, such as adiposity-based chronic disease (ABCD), reflect the complexity of obesity and connect diagnosis more closely to health outcomes 14 15. |
How have obesity rates changed in the U.S., and what factors drive increases?
Multiple studies document a sustained and dramatic rise in U.S. obesity prevalence over recent decades, showing parallel increases in both moderate and severe obesity. The new study’s finding—that nearly 70% of adults could be classified as obese under updated criteria—aligns with long-term projections and highlights the growing scale of the challenge, particularly among older adults and vulnerable subgroups.
- Obesity prevalence among U.S. adults increased from 13% in the 1960s to over 30% by 2004, with projections exceeding 50% by 2030 when using BMI-based definitions 1 3.
- Rates have increased more rapidly among women, non-Hispanic Black adults, and individuals with lower socioeconomic status 1 2 3 4.
- Severe obesity (e.g., BMI ≥40) is rising faster than moderate obesity, with the heaviest groups expanding most rapidly 5.
- The new study’s estimate—nearly 70% classified as obese under expanded criteria—exceeds previous BMI-based projections, reflecting the impact of broader measurement approaches.
What are the health consequences of obesity, especially regarding fat distribution?
A substantial body of research shows that the health risks associated with obesity depend not only on total body fat, but also on its distribution—especially abdominal or visceral fat. The expanded definition used in the new study, which incorporates anthropometric measures beyond BMI, is supported by evidence linking central obesity with increased risks of diabetes, cardiovascular disease, and mortality.
- Abdominal (central) obesity is more strongly associated with metabolic and cardiovascular complications than overall BMI 7 8 13 14.
- Childhood and adult obesity are both linked to long-term morbidity, including diabetes, hypertension, heart disease, cancer, and reduced life expectancy 6 8 9 10.
- Visceral fat, as measured by waist circumference or waist-to-hip ratio, is a critical predictor of health risk, and is not captured by BMI alone 7 8 12 13 14.
- The new study’s observation that newly classified individuals (with normal BMI but high abdominal fat) have elevated risks is consistent with these literature findings.
How do changes in obesity definitions or classification criteria affect prevalence and diagnosis?
Recent literature suggests that evolving obesity definitions—especially those that include direct or indirect measures of body fat and its distribution—result in higher prevalence estimates and more accurate identification of at-risk individuals. The new study provides large-scale evidence of the impact such changes can have on population health statistics and clinical practice.
- Transitioning from BMI-only criteria to those including anthropometric or metabolic factors increases the number of individuals classified as obese, particularly among older adults and specific demographic groups 11 12 13 14 15.
- Definitions such as adiposity-based chronic disease (ABCD) and criteria emphasizing fat distribution or disease burden are being adopted to reflect the complexity of obesity and its health impacts 12 14 15.
- Newer guidelines, such as those from the Korean Society for the Study of Obesity and international expert panels, increasingly emphasize morbidity and fat distribution for diagnosis 14 15.
- The study’s findings about the sharp rise in prevalence and risk underscore the practical consequences of adopting broader diagnostic frameworks.
Future Research Questions
The expanded definition of obesity marks a significant shift in how risk is identified and managed, but it also raises important questions for future research. Further investigation is needed to understand which subgroups are most affected, how best to target interventions, and what long-term health and economic impacts may arise from reclassifying such a large segment of the population.
| Research Question | Relevance |
|---|---|
| What are the long-term health outcomes for individuals with anthropometric-only obesity? | Understanding the specific risks and disease trajectories for this newly classified group can inform screening, prevention, and treatment strategies 6 8 9. |
| How do different obesity definitions influence treatment eligibility and outcomes? | Comparing health outcomes across classification systems can help refine guidelines for medication, surgery, and lifestyle interventions 12 14 15. |
| What are the biological and sociodemographic determinants of anthropometric-only obesity? | Identifying risk factors unique to this group may reveal new prevention opportunities and address disparities 1 3 4. |
| How cost-effective are expanded screening and treatment strategies under the new obesity definition? | Evaluating the economic and public health impact of broader classification can guide policy decisions and resource allocation 9 10. |
| What are the psychosocial effects of reclassifying a larger population as obese? | Understanding potential consequences of labeling, stigma, or insurance changes is important for patient well-being and public health messaging 8 9. |
This evidence-based overview highlights the sharp rise in U.S. obesity rates under updated definitions and underscores the need for continued research to guide prevention, diagnosis, and treatment in a changing clinical and public health landscape.