New definition of obesity
The World Health Organization (WHO) has long classified obesity as a disease. Nevertheless, it is disputed whether obesity is truly an independent disease or rather a risk factor for other diseases.
In early 2025, an international commission launched by The Lancet Diabetes & Endocrinology proposed classifying obesity into two categories: Preclinical and clinical obesity. In line with this concept, obesity should be confirmed by at least one other anthropometric criterion, such as waist circumference or body fat content, in addition to BMI. Accordingly, people with diagnosed obesity who also have obesity-related abnormalities, such as high blood pressure or disorders of glucose and lipid metabolism, should be classified as clinically obese, and obese people without these abnormalities as preclinical. The commission proposes classifying clinical obesity as an independent disease with corresponding treatment indications.
Evaluation of large population and interventional studies
Against this backdrop, scientists from the German Center for Diabetes Research (DZD), DIfE, and the University Hospital Tübingen have explored how frequently preclinical and clinical obesity occur in the population, whether affected individuals have an increased risk of type 2 diabetes and cardiovascular disease, and whether a lifestyle intervention can reduce the prevalence of clinical obesity. To do so, the researchers evaluated the data from three major studies: The National Health and Nutrition Examination Survey (NHANES; representative of the U.S. Population), the European Prospective Investigation into Cancer and Nutrition (EPIC) Potsdam Study, and the Tuebingen Lifestyle Intervention Program (TULIP).
Differences in risk: preclinical versus clinical obesity
In the process, it was demonstrated that 100 percent of people with a BMI equal to or greater than 30 kg/m² could be classified as obese based on at least one other anthropometric criterion. Furthermore, around 80 percent met the criteria for clinical obesity.
People with clinical obesity had an approximately 3-times higher risk of cardiovascular disease and a roughly 8-times higher risk of type 2 diabetes compared with people who do not have obesity and do not meet the clinical criteria. In contrast, people with preclinical obesity did not exhibit an increased risk of cardiovascular disease but still had an increased risk of type 2 diabetes.
A nine-month lifestyle intervention in the TULIP study lowered the rate of clinical obesity from 71 to 57 percent and the rate of prediabetes from 52 to 29 percent. The scientists determined that blood pressure, triglyceride levels, and blood sugar regulation were particularly improved by the intervention. “This is an important prerequisite for possible prevention strategies in this context,” explains Prof. Norbert Stefan from the University Hospital Tübingen. How well people respond to a lifestyle program appears to be dependent on age and liver fat content, among other things.
Additional diagnostic steps are not always necessary
“Our results provide a solid data basis for evaluating this newly proposed definition,” says first author Dr. Catarina Schiborn from DIfE. “We were able to demonstrate that an additional confirmation of obesity through further anthropometric measurements such as waist circumference or body fat content, as proposed by the commission as a first diagnostic step, does not appear to be necessary in practice, as they were met by virtually all participants with a BMI-based obesity status. In this regard, further refinement of these additional criteria is needed.“
Furthermore, less than 20 percent of people with confirmed obesity would be considered preclinical. Most people with obesity already exhibit measurable health impairments and are therefore classified as having clinical obesity. “We also observed that many clinical criteria strongly overlap,” adds Prof. Matthias Schulze, head of the Department of Molecular Epidemiology at DIfE. “This raises the question of whether such a comprehensive diagnosis process for the classification of preclinical and clinical obesity is actually necessary.“
In further studies, the researchers want to compare the new criteria with already established concepts such as “metabolically healthy” versus “metabolically unhealthy“ obesity.
Original publication:
Schiborn, C., Hu, F., Stefan, N., Schulze, M.: Preclinical and clinical obesity: prevalence, associations to cardiometabolic risk and response to lifestyle intervention in NHANES and the EPIC-Potsdam and TULIP studies. Nature Commun. 17, 1935 (2026). [Open Access]
Further publications:
Schulze, M. B., Stefan, N.: Metabolically healthy obesity: from epidemiology and mechanisms to clinical implications. Nat. Rev. Endocrinol. 20, 633–646 (2024). [Open Access]
Stefan, N., Schulze, M. B.: Metabolic health and cardiometabolic risk clusters: implications for prediction, prevention, and treatment. Lancet Diabetes Endocrinol. 11(6), 426-440 (2023).
Zembic, A., Eckel, N., Stefan, N., Baudry, J., Schulze, M. B.: An Empirically Derived Definition of Metabolically Healthy Obesity Based on Risk of Cardiovascular and Total Mortality. JAMA Netw. Open 4(5), e218505 (2021). [Open Access]
Background information
Obesity was first recognized as a disease by the WHO in 1948, and more recently also by several medical societies and countries. The current International Classification of Diseases (ICD) published by the WHO defines obesity as a “chronic complex disease“ and assigns it a specific code (5B81). Nevertheless, it is disputed whether obesity is truly an independent disease or rather a risk factor for other diseases.
Advocates say:
If obesity is officially recognized as a disease, affected individuals would have better access to medical assistance. It could also help to eliminate prejudice and stigma.
Critics warn:
A blanket definition of obesity as a disease could diminish personal responsibility. Moreover, not all people with overweight are unhealthy. The common measurement of BMI says little about the individual’s actual health status. Such a classification could lead to overdiagnosis—with unnecessary medication, surgery, and high costs.
The core issue is:
The specific illness caused by obesity itself has not yet been clearly defined. In most cases, it is merely regarded as a trigger for other diseases (e.g., type 2 diabetes, cardiovascular disease), rather than as a disease with distinct symptoms. It therefore lacks a clear medical identity.
In addition, overweight can have very wide-ranging causes and meanings, sometimes even being labeled as a symptom of other diseases. The current definition of obesity is therefore often imprecise for medical decisions.
At the same time, this lack of clarity means that many affected individuals receive no treatment because they “have yet developed a secondary condition“—even though their body is already impaired by the overweight.
The new diagnosis criteria proposed by the Lancet expert commission are intended to improve the assessment of obesity in everyday medical practice—not only with regard to bodyweight, but also specific health impairments in areas such as respiration, metabolism, the cardiovascular system, organ systems (e.g., liver and kidneys), or the musculoskeletal system. If overweight has already caused measurable damage to organs and tissues, the commission defines it as “clinical obesity.” Without such restrictions, obesity is considered “preclinical.”
Such a new understanding could:
- allow for more equitable medical care,
- support better political decision-making,
- and improve social attitudes to obesity.
Further information:
Rubino, F. et al.: Definition and diagnostic criteria of clinical obesity. Lancet Diabetes Endocrinol. 13(3), 221-262 (2025). [Open Access]
Scientific contact:
Prof. Dr. Matthias Schulze
Head of the Department of Molecular Epidemiology at DIfE
Phone: +49 33 200 88 - 2434
E-Mail: mschulze@dife.de
Dr. Catarina Schiborn
Postdoc of the Department of Molecular Epidemiology at DIfE
Phone: +49 33 200 88 – 2526
E-Mail: catarina.schiborn@dife.de
Prof. Dr. Norbert Stefan
Professorship for Clinical and Experimental Diabetology at University Hospital Tübingen
Phone: +49 7071 2980390
E-Mail: norbert.stefan@med.uni-tuebingen.de
Press contact:
PR at the DIfE
Phone: +49 33200 88 - 2335
E-Mail: presse@dife.de
The German Institute of Human Nutrition Potsdam-Rehbruecke (DIfE) is a member of the Leibniz Association. It investigates the causes of nutrition-associated diseases in order to develop new strategies for prevention, treatment and nutritional recommendations. Its research interests include the causes and consequences of the metabolic syndrome, a combination of obesity, hypertension (high blood pressure), insulin resistance and lipid metabolism disorder, the role of nutrition for healthy aging and the mechanisms of food choice and precision nutrition. DIfE is also a partner of the German Center for Diabetes Research (DZD), which has been funded by the Federal Ministry of Research, Technology and Space (BMFTR) since 2009. https://www.dife.de/en
The German Center for Diabetes Research (DZD) is a national association that brings together experts in the field of diabetes research and combines basic research, translational research, epidemiology and clinical applications. The aim is to develop novel strategies for personalized prevention and treatment of diabetes. Members are Helmholtz Munich – German Research Center for Environmental Health, the German Diabetes Center in Düsseldorf, the German Institute of Human Nutrition in Potsdam-Rehbrücke, the Paul Langerhans Institute Dresden of Helmholtz Munich at the University Medical Center Carl Gustav Carus of the TU Dresden and the Institute for Diabetes Research and Metabolic Diseases of Helmholtz Munich at the Eberhard-Karls-University of Tuebingen together with associated partners at the Universities in Heidelberg, Cologne, Leipzig, Lübeck and Munich. www.dzd-ev.de/en
