An international research group has examined how many people are affected by preclinical and clinical obesity and what health risks are associated with this. The team led by Prof. Matthias Schulze from the German Institute of Human Nutrition Potsdam-Rehbruecke (DIfE) discovered that almost all people with obesity, i.e., a body mass index (BMI) of at least 30 kg/m², exhibit other measurable indications of increased body fat mass and that around 80 percent of affected individuals are already experiencing health-related complications. The results have been published in the specialist journal Nature Communications .
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. According to 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. Furthermore, people with diagnosed obesity who also show obesity-related abnormalities, such as high blood pressure or disorders of glucose and lipid metabolism, should be classified as having clinical obesity, and people without these abnormalities as having preclinical obesity. The commission proposes classifying clinical obesity as an independent disease with corresponding treatment indications.
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).
In the process, it was demonstrated that 100 percent of people with a BMI equal to or greater than 30 kg/m² could be confirmed as having obesity 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.
“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.
Backround 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:
Further Information
Rubino, F. et al.: Definition and diagnostic criteria of clinical obesity. Lancet Diabetes Endocrinol. 13(3), 221-262 (2025). [Open Access]
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]
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]
Nature Communications
Observational study
People
Preclinical and clinical obesity: prevalence, associations to cardiometabolic risk and response to lifestyle intervention in NHANES and the EPIC-Potsdam and TULIP studies
19-Feb-2026