New Study on Obesity Criteria Shows: Vast Majority of Affected Individuals are Classified as Clinically Obese

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.

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. 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.

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 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.

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. 

 

Scientific Contacts

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

Press and Public Relations at DIfE
phone: +49 33200 88 - 2335
e-mail: presse@dife.de

 

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