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Obesity is linked to many common diseases, such as type 2 diabetes, heart disease, fatty liver disease and knee osteoarthritis.
Obesity is currently defined using a person’s body mass index, or BMI. This is calculated as weight (in kilograms) divided by the square of height (in metres). In people of European descent, the BMI for obesity is 30 kg/m² and over.
But the risk to health and wellbeing is not determined by weight – and therefore BMI – alone. We’ve been part of a global collaboration that has spent the past two years discussing how this should change. Today we publish how we think obesity should be defined and why.
As we outline in The Lancet, having a larger body shouldn’t mean you’re diagnosed with “clinical obesity”. Such a diagnosis should depend on the level and location of body fat – and whether there are associated health problems.
What’s wrong with BMI?
The risk of ill health depends on the relative percentage of fat, bone and muscle making up a person’s body weight, as well as where the fat is distributed.
Athletes with a relatively high muscle mass, for example, may have a higher BMI. Even when that athlete has a BMI over 30 kg/m², their higher weight is due to excess muscle rather than excess fatty tissue.
People who carry their excess fatty tissue around their waist are at greatest risk of the health problems associated with obesity.
Fat stored deep in the abdomen and around the internal organs can release damaging molecules into the blood. These can then cause problems in other parts of the body.
But BMI alone does not tell us whether a person has health problems related to excess body fat. People with excess body fat don’t always have a BMI over 30, meaning they are not investigated for health problems associated with excess body fat. This might occur in a very tall person or in someone who tends to store body fat in the abdomen but who is of a “healthy” weight.
On the other hand, others who aren’t athletes but have excess fat may have a high BMI but no associated health problems.
BMI is therefore an imperfect tool to help us diagnose obesity.
What is the new definition?
The goal of the Lancet Diabetes & Endocrinology Commission on the Definition and Diagnosis of Clinical Obesity was to develop an approach to this definition and diagnosis. The commission, established in 2022 and led from King’s College London, has brought together 56 experts on aspects of obesity, including people with lived experience.
The commission’s definition and new diagnostic criteria shifts the focus from BMI alone. It incorporates other measurements, such as waist circumference, to confirm an excess or unhealthy distribution of body fat.
We define two categories of obesity based on objective signs and symptoms of poor health due to excess body fat.
1. Clinical obesity
A person with clinical obesity has signs and symptoms of ongoing organ dysfunction and/or difficulty with day-to-day activities of daily living (such as bathing, going to the toilet or dressing).
There are 18 diagnostic criteria for clinical obesity in adults and 13 in children and adolescents. These include:
- breathlessness caused by the effect of obesity on the lungs
- obesity-induced heart failure
- raised blood pressure
- fatty liver disease
- abnormalities in bones and joints that limit movement in children.
2. Pre-clinical obesity
A person with pre-clinical obesity has high levels of body fat that are not causing any illness.
People with pre-clinical obesity do not have any evidence of reduced tissue or organ function due to obesity and can complete day-to-day activities unhindered.
However, people with pre-clinical obesity are generally at higher risk of developing diseases such as heart disease, some cancers and type 2 diabetes.
What does this mean for obesity treatment?
Clinical obesity is a disease requiring access to effective health care.
For those with clinical obesity, the focus of health care should be on improving the health problems caused by obesity. People should be offered evidence-based treatment options after discussion with their health-care practitioner.
Treatment will include management of obesity-associated complications and may include specific obesity treatment aiming at decreasing fat mass, such as:
- support for behaviour change around diet, physical activity, sleep and screen use
- obesity-management medications to reduce appetite, lower weight and improve health outcomes such as blood glucose (sugar) and blood pressure
- metabolic bariatric surgery to treat obesity or reduce weight-related health complications.
Should pre-clinical obesity be treated?
For those with pre-clinical obesity, health care should be about risk-reduction and prevention of health problems related to obesity.
This may require health counselling, including support for health behaviour change, and monitoring over time.
Depending on the person’s individual risk – such as a family history of disease, level of body fat and changes over time – they may opt for one of the obesity treatments above.
Distinguishing people who don’t have illness from those who already have ongoing illness will enable personalised approaches to obesity prevention, management and treatment with more appropriate and cost-effective allocation of resources.
What happens next?
These new criteria for the diagnosis of clinical obesity will need to be adopted into national and international clinical practice guidelines and a range of obesity strategies.
Once adopted, training health professionals and health service managers, and educating the general public, will be vital.
Reframing the narrative of obesity may help eradicate misconceptions that contribute to stigma, including making false assumptions about the health status of people in larger bodies. A better understanding of the biology and health effects of obesity should also mean people in larger bodies are not blamed for their condition.
People with obesity or who have larger bodies should expect personalised, evidence-based assessments and advice, free of stigma and blame.
Louise Baur is a Professor with the Discipline of Child and Adolescent Health at University of Sydney.
John B. Dixon is an Adjunct Professor with the Iverson Health Innovation Research Institute, Swinburne University of Technology.
Priya Sumithran is Head of the Obesity and Metabolic Medicine Group in the Department of Surgery at School of Translational Medicine, Monash University.
Wendy A. Brown is a Professor and Chair of Monash University Department of Surgery, School of Translational Medicine, Alfred Health, Monash University.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
The statements or opinions expressed in this article reflect the views of the authors and do not necessarily represent the official policy of the AMA, the MJA or InSight+ unless so stated.
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Excessive weight gain is a common side effect of psychotropic medications as used for patients in treatment of mental illness. The weight gain is usually relatively rapid, over several months, and mainly occurs in the abdominal region. Patients may be told by clinicians that they need to diet, even by a consultant psychiatrist. The consequences of psychotropic medication use on physical health and life expectancy is a serious topic worthy of further investigation
I am not quite sure how this would help me in my consult at all …. Is this honestly about ‘ healthy obese’ people like weight lifters etc not having to be called obese/ talk about risks etc ?? This is a minor group, the majority either HAS already complications or is on the road to them. Is this about resource allocation ? you are clinically obese you get medication/surgery/support etc – and you poor thing are not there yet, you get ‘only’ the pep talk.
I feel I am missing why suddenly everyone is so excited about the new classification. By the way I LOVE the responses above.
Obesity is not a perjorative word, just as hypertension is not a perjorative word, well at least I used to think so.
To compare with BP –
We don’t wait for a patient to develop headache, stroke, CCF or CKD before starting to treat elevated BP seriously.
But now we can, because we can divide them into having pre-clinical hypertension and clinical hypertension- even if both groups have the same BP of 180/100. Excellent development. I am loving this new classification which really makes sense to doctors and patient!
NOW we can have a pre- clinical pregnancy ( one that is not associated with any complications) or
a clinical pregnancy (eg a pregnancy that is associated with diabetes, hypertension, hyperemesis, bleeding and fatigue. etc ) Please do let me know when the threshold for clinical pregnancy is achieved, as there are going to be some big surprises in 9 months, fo patients with pre clinical pregnancies, for sure.
Now we can have pre clinical AMI’s ( eg old infarct picked up on an ECG) – this is great news because if our patient never had any symptoms I don’t have to do anything about their cholesterol etc now. I can just wait for other things to happen. Yippee!
Anorexia can now be classified a pre-clinical even if a patient has a BMI of 14 , and they swear that they feel fine (as they often do) and especially their BP and heart rate is just hanging in there, We can now classify them as a healthy anorexics, and both the patient and my own stress levels will go down enormously. Fabulous.
NOW we can have pre clinical smokers, whom we can call healthy smokers. I like to use the term- People living with smoking. We can then really start to implement serious treatment once they become clinical smokers – now I can wait for COPD, IHD, SOB and lung cancer to develop. before offering champix. Win-Win.
Once again, less work for poor GPs who are focusing on prevention, more work for doctors who treat people after the proverbial clinical horse has bolted. We really need more clinical guidelines such as these Happy days!
Moving away from simplistic yardsticks that mainly work at the population level is laudable.
A more personalized, differentiated approach is inherently preferable – as long as the resources are there to deliver it to all.
There is also a risk in trying too much to avoid “stigmatizing obesity”: it can lead to the normalization of obesity, a literally unhealthy outcome. Some medical home truths need to be delivered in clear, unvarnished language, while an overly softened language can create a false impression.
Redefining obesity using new criteria incorporating clinical and pre-clinical categories raises concerns about equity, stigma, and resource allocation, particularly when viewed through the lens of diversity, equity, and inclusion (DEI). While Benjamin Franklin’s maxim, “To lengthen thy life, lessen thy meals,” underscores the importance of personal responsibility and prevention, the proposed changes risk shifting focus toward complex diagnostics and medical interventions, potentially sidelining preventive public health strategies. This may exacerbate disparities, as communities with limited resources might struggle to access advanced diagnostic tools and personalized treatments. Introducing nuanced classifications could unintentionally reinforce stigma and cultural biases, especially for ethnic groups with unique body composition patterns. Furthermore, the increased complexity and cost of care may divert resources from scalable initiatives, like dietary education and community fitness programs, which are more inclusive and effective for population health. To reduce stigma and promote health equity, a balanced approach that prioritizes accessible prevention strategies and empowers individuals to take responsibility for their health is essential.
Hopefully a systemic review on the issues of obesity will be published soon from our think tank (ESJ).
Obesity is a state that is originally defined by BMI calculation.
Advocates and revisionists invariably talk about the “healthy obese”, in which there is no discernable disease apparent in these people.
The fact is it takes years to develop disease, and it is not always accepted by those who have the disease that it is an attribute of their obesity.
Being obesity cannot be normal state, whereby in a generation or two, the proportion of those that qualify as obesity by BMi, is doubled.
SImilarly obesity being linked with increased musculoskeletal pathology, anaesthetic risk and post operative complications, points to the status not consistent with “healthy”.
BMi doesnt fat shame, neither does the word “obese”, people do. If we now suddenly decide that it is “ok” or even normal/acceptable to be obese, in whatever descriptive we use (for example “pre-clinical obesity”) we are just letting emotions and shaming-avoidance run the show, but ultimately we will still end up in a full cycle in 20 years time that obesity is not a normal state, whatever gene we may inherit or blame.
Why is the full article in Lancet Endocrinology not Open Access? Difficult to scrutinise and learn.