KU and Harvard University: Normal Weight Doesn’t Mean Safe — 45% of U.S. Adults “Clinically Obese”

New definition of clinical obesity reveals hidden high-risk groups, posing new challenges for healthcare and insurance systems.

△ (From left) Research Professor Park Da-hyun (first author) at KU Institute for BioMaterials, Professor Shin Min-jeong (corresponding author) of the School of Biosystem and Biomedical Science, and Professor S. V. Subramanian (co-corresponding author) of the T.H.CHAN School of Public Health at Harvard University

Professor Shin Min-jeong of the School of Biosystems and Biomedical Science at KU (President: Kim Dong-One), in collaboration with a research team from Harvard University, has announced research findings indicating that approximately 45% of U.S. adults fall under the newly defined category of “clinical obesity.” This study indicates that body weight indices alone are insufficient for accurately identifying obesity.

The results of this study were published online on September 26 in JAMA Network Open (IF=9.7, JCR top 4.1%), an international journal in the field of medicine.

*Article title : Prevalence of Clinical Obesity in US Adults Based on a Newly Proposed Definition

*DOI: 10.1001/jamanetworkopen.2025.33806

The joint research team analyzed data from the US National Health and Nutrition Examination Survey (NHANES), comparing the conventional body mass index (BMI) criteria with the newly proposed definition of “clinical obesity” presented by The Lancet Diabetes & Endocrinology Commission. The concept of “clinical obesity” represents a new classification system that considers not only BMI but also metabolic dysfunction, organ impairment, and reduced daily living function due to excessive fat accumulation.

The analysis revealed that while the obesity rate based on BMI was 43.8% and the rate of clinical obesity was 44.7%, only 25.8% of individuals met both criteria. In other words, a considerable proportion of those classified as obese by BMI did not exhibit clinical complications, whereas a notable number of individuals within the normal weight range exhibited metabolic problems, organ impairment, or functional decline.

Age-related patterns also varied significantly. Among older adults, many were classified as clinically obese despite having relatively low BMI values, due to metabolic dysfunction or decline in physical functioning. On the other hand, a considerable number of younger adults with high BMI did not exhibit clinical abnormalities. These findings indicate that the concept of clinical obesity effectively identifies high-risk groups that may not be detected through body weight measurements alone.

The research team underscored that these results are significant for medical practice and health policy. With the recent global development of new drugs, including GLP-1-based obesity treatments, a new definition of obesity could serve as a more precise criterion for identifying those in need of treatment.

The redefinition of obesity as a clinical disease rather than merely a weight issue is expected to have far-reaching impacts on future health insurance coverage and access to treatment, and the expansion of the global obesity therapeutics market.

KU Professor Shin Min-jeong emphasized, “The key lies not only in weight reduction but also in managing body fat and preserving physical functions. Our findings are expected to broadly affect future strategies for the diagnosis, treatment, and prevention of obesity.”

This study was supported by the National Research Foundation of Korea.