Commission Issues ‘Radical Overhaul’ of Obesity Diagnosis

A Lancet Commission has redefined obesity by classifying it as either “clinical obesity,” a disease, or “preclinical,” a health risk factor, with the distinction based on factors beyond body mass index (BMI).

“We propose a radical overhaul of the actual diagnosis of obesity to improve global healthcare and practices and policies. The specific aims were to facilitate individualized assessment and care of people living with obesity while preserving resources by reducing overdiagnosis and unnecessary or inadequate interventions,” Professor Louise Baur, chair of Child & Adolescent Health at the University of Sydney, Sydney, Australia, said during a UK Science Media Centre (SMC) news briefing.

The report calls first for a diagnosis of obesity via confirmation of excess adiposity using measures such as waist circumference or waist-to-hip ratio in addition to BMI. Next, a clinical assessment of signs and symptoms of organ dysfunction due to obesity and/or functional limitations determines whether the individual has the disease “clinical obesity,” or “preclinical obesity,” a condition of health risk but not an illness itself.

Published on January 14, 2025, in TheLancet Diabetes & Endocrinology, the document also provides broad guidance on management for the two obesity conditions, emphasizing a personalized and stigma-free approach. The Lancet Commission on Obesity comprised 56 experts in relevant fields including endocrinology, surgery, nutrition, and public health, along with people living with obesity.

The report has been endorsed by more than 75 medical organizations, including the Association of British Clinical Diabetologists, the American Association of Clinical Endocrinologists, the American Diabetes Association, the American Heart Association, the Obesity Society, the World Obesity Federation, and obesity and endocrinology societies from countries in Europe, Latin America, Asia, and South Africa.

In recent years, many in the field have found fault with the current BMI-based definition of obesity (> 30 for people of European descent or other cutoffs for specific ethnic groups), primarily because BMI alone doesn’t reflect a person’s fat vs lean mass, fat distribution, or overall health. The new definition aims to overcome these limitations, as well as settle the debate about whether obesity is a “disease.”

“We now have a clinical diagnosis for obesity, which has been lacking…The traditional classification based on BMI…reflects simply whether or not there is excess adiposity, and sometimes not even precise in that regard, either…It has never been a classification that was meant to diagnose a specific illness with its own clinical characteristics in the same way we diagnose any other illness,” Commission Chair Francesco Rubino, MD, professor and chair of Metabolic and Bariatric Surgery at King’s College London, England, told Medscape Medical News.

He added, “The fact that now we have a clinical diagnosis allows recognition of the nuance that obesity is generally a risk and for some can be an illness. There are some who have risk but don’t have the illness here and now. And it’s crucially important for clinical decision-making, but also for policies to have a distinction between those two things because the treatment strategy for one and the other are substantially different.”

Asked to comment, obesity specialist Michael A. Weintraub, MD, clinical assistant professor of endocrinology at New York University Langone Health, told Medscape Medical News, “I wholeheartedly agree with modifying the definition of obesity in this more accurate way…There has already been a lot of talk about the fallibility of BMI and that BMI over 30 does not equal obesity…So a major Commission article like this I think can really move those discussions even more into the forefront and start changing practice.” 

However, Weintraub added, “I think there needs to be another step here of more practical guidance on how to actually implement this…including how to measure waist circumference and to put it into a patient flow.” Asked to comment, obesity expert Luca Busetto, MD, associate professor of internal medicine at the Department of Medicine of the University of Padova, Padova, Italy, told Medscape Medical News that he agrees with the general concept of moving beyond BMI in defining obesity. That view was expressed in a proposed “framework” from the European Association for the Study of Obesity (EASO), for which Busetto was the lead author.

Busetto also agrees with the emphasis on the need for a complete clinical evaluation of patients to define their health status. “The precise definition of the symptoms defining clinical obesity in adults and children is extremely important, emphasizing the fact that obesity is a severe and disabling disease by itself, even without or before the occurrence of obesity-related complications,” he said.

However, he takes issue with the Commission’s designation that “preclinical” obesity is not a disease. “The critical point of disagreement for me is the message that obesity is a disease only if it is clinical or only if it presents functional impairment or clinical symptoms. This remains, in my opinion, an oversimplification, not taking into account the fact that the pathophysiological mechanisms that lead to fat accumulation and ‘adipose tissue-based chronic disease’ usually start well before the occurrence of symptoms.”

Busetto pointed to examples such as type 2 diabetes and chronic kidney disease, both of which can be asymptomatic in their early phases yet are still considered diseases at those points. “I have no problem in accepting a distinction between preclinical and clinical stages of the disease, and I like the definition of clinical obesity, but why should this imply the fact that obesity is NOT a disease since its beginning?”

The Commission does state that preclinical obesity should be addressed, mostly with preventive approaches but in some cases with more intensive management. “This is highly relevant, but the risk of an undertreatment of obesity in its asymptomatic state remains in place. This could delay appropriate management for a progressive disease that certainly should not be treated only when presenting symptoms. It would be too late,” Busetto said.

And EASO framework co-author Gijs Goossens, PhD, professor of cardiometabolic physiology of obesity at Maastricht University Medical Centre, the Netherlands, added a concern that those with excess adiposity but lower BMI might be missed entirely, noting “Since abdominal fat accumulation better predicts chronic cardiometabolic diseases and can also be accompanied by clinical manifestations in individuals with overweight as a consequence of compromised adipose tissue function, the proposed model may lead to underdiagnosis or undertreatment in individuals with BMI 25-30 who have excess abdominal fat.”

Diagnosis and Management Beyond BMI

The Commission advises the use of BMI solely as a marker to screen for potential obesity. Those with a BMI > 40 can be assumed to have excess body fat. For others with a BMI at or near the threshold for obesity in a specific country or ethnic group or for whom there is the clinical judgment of the potential for clinical obesity, confirmation of excess or abnormal adiposity is needed by one of the following:

• At least one measurement of body size and BMI
• At least two measures of body size, regardless of BMI
• Direct body fat measurement, such as a dual-energy x-ray absorptiometry (DEXA) scan

Measurement of body size can be assessed in three ways: 

• Waist circumference ≥ 102 cm for men and ≥ 88 cm for women
• Waist-to-hip ratio > 0.90 for men and > 0.50 for women
• Waist-to-height ratio > 0.50 for all.

Weintraub noted, “Telemedicine is a useful tool used by many patients and providers but may also make it challenging to accurately assess someone’s body size. Having technology like an iPhone app to measure body size would circumvent this challenge but this type of tool has not yet been validated.” 

If the person does not have excess adiposity, they don’t have obesity. Those with excess adiposity do have obesity. Further assessment is then needed to establish whether the person has an illness, that is, clinical obesity, indicated by signs/symptoms of organ dysfunction, and/or limitations of daily activities. If not, they have “preclinical” obesity.

The document provides a list of 18 obesity-related organ, tissue, and body system criteria for diagnosing “clinical” obesity in adults, including upper airways (eg, apneas/hypopneas), respiratory (breathlessness), cardiovascular (hypertension, heart failure), liver (fatty liver disease with hepatic fibrosis), reproductive (polycystic ovary syndrome, hypogonadism), and metabolism (hyperglycemia, hypertriglyceridemia, low high-density lipoprotein cholesterol). A list of 13 such criteria is also provided for children. “Limitations of day-to-day activities” are included on both lists.

Management Differs by Designation

For preclinical obesity, management should focus on risk reduction and prevention of progression to clinical obesity or other obesity-related diseases. Such approaches include health counseling for weight loss or prevention of weight gain, monitoring over time, and active weight loss interventions in people at higher risk of developing clinical obesity and other obesity-related diseases.

Management for clinical obesity focuses on improvements or reversal of the organ dysfunction. The type of evidence-based treatment and management should be informed by individual risk-benefit assessments and decided via “active discussion” with the patient. Success is determined by improvement in the signs and symptoms rather than measures of weight loss.

In response to a reporter’s question at the SMC briefing about the implications for the use of weight-loss medications, Rubino noted that this wasn’t the focus of the report, but nonetheless said that this new obesity definition could help with their targeted use. “The strategy and intent by which you use the drugs is different in clinical and preclinical obesity…Pharmacological interventions could be used for patients with high-risk preclinical obesity, with the intent of reducing risk, but we…would use the same medication at a different intensity, dose, and maybe in combination therapies.”

As for clinical obesity, “It could be more or less severe and could affect more than one organ, and so clinical obesity might require drugs, might require surgery, or may require, in some cases, a combination of both of them, to achieve the best possible outcomes…We want to make sure that the person is restoring health…with whatever it takes.”

Rubino believes this new definition will convince the remaining clinicians who haven’t yet accepted the concept of obesity as a disease. “When they see clinical obesity, I think it will be much harder to say that a biological process that is capable of causing a dysfunction in the heart or the lungs is less of a disease than another biological process that causes similar dysfunction in the heart of the lungs…It’s going to be objective. Obesity is a spectrum of different situations…When it’s an illness, clinical obesity, it’s not a matter of if or when. It’s a matter of fact.”

There were no industrial grants or other funding for this initiative. King’s Health Partners hosted the initiative and provided logistical and personnel support to facilitate administrative work and the Delphi-like consensus-development process.

Rubino declared receiving research grants from Ethicon (Johnson & Johnson), Novo Nordisk, and Medtronic; consulting fees from Morphic Medical; speaking honoraria from Medtronic, Ethicon, Novo Nordisk, Eli Lilly, and Amgen. Rubino has served (unpaid) as a member of the scientific advisory board for Keyron and a member of the data safety and monitoring board for GI Metabolic Solutions; is president of the Metabolic Health Institute (non-profit); and is the sole director of Metabolic Health International and London Metabolic and Bariatric Surgery (private practice).

Baur declared serving on the scientific advisory board for Novo Nordisk (for the ACTION Teens study) and Eli Lilly and receivingspeaker fees (paid to the institution) from Novo Nordisk.

Miriam E. Tucker is a freelance journalist based in the Washington DC area. She is a regular contributor to Medscape, with other work appearing in the Washington Post, NPR’s Shots blog, and Diatribe. She is on X @MiriamETucker.