With over one billion people in the world now estimated to be living with obesity, there is an urgent need for health systems globally to adopt a universal, clinically relevant definition and diagnosis of obesity.
Endorsed by 76 medical organisations around the world, The Lancet Diabetes & Endocrinology Commission sets out a new diagnostic model of obesity based on objective measures of illness at the individual level and introduces two novel categories of obesity – clinical obesity and pre-clinical obesity.
This Commission was organised as a partnership between the medical journal The Lancet Diabetes & Endocrinology and King’s Health Partners (KHP) Diabetes, Endocrinology and Obesity. It was chaired by Prof Francesco Rubino, Chair of Metabolic and Bariatric Surgery in the Faculty of Life Sciences and Medicine, King's College London, and Honorary Consultant at King's College Hospital NHS Foundation Trust.
Key findings
Current medical approaches to diagnosing obesity rely on body mass index (BMI) which is not a reliable measure of health or illness at the individual level. This can result in misdiagnosis, with negative consequences for people living with obesity and our wider society.
The Commission on Clinical Obesity recommends a new, nuanced approach where measures of body fat - for example, waist circumference or direct fat measurement - in addition to BMI are used to detect obesity, therefore reducing the risk of misclassification.
Additionally, the authors introduce two new diagnostic categories of obesity based on objective measures of illness at the individual level; ‘clinical obesity’ (a chronic disease associated with ongoing organ dysfunction due to obesity alone) and ‘pre-clinical obesity’ (associated with a variable level of health risk, but no ongoing illness).
The Commission authors call for all people living with obesity to receive personalised health advice and evidence-based care when needed - free of stigma and blame - with different strategies for those with clinical obesity and pre-clinical obesity.
Prof Francesco Rubino, Commission Chair based at King's College London, says:
“The question of whether obesity is a disease is flawed because it presumes an implausible all-or-nothing scenario where obesity is either always a disease or never a disease. Evidence, however, shows a more nuanced reality. Some individuals with obesity can maintain normal organs’ function and overall health, even long term, whereas others display signs and symptoms of severe illness here and now.
“Considering obesity only as a risk factor, and never a disease, can unfairly deny access to time-sensitive care among people who are experiencing ill health due to obesity alone. On the other hand, a blanket definition of obesity as a disease can result in overdiagnosis and unwarranted use of medications and surgical procedures, with potential harm to the individual and staggering costs for society.
“Our reframing acknowledges the nuanced reality of obesity and allows for personalised care. This includes timely access to evidence-based treatments for individuals with clinical obesity, as appropriate for people suffering from a chronic disease, as well as risk-reduction management strategies for those with pre-clinical obesity, who have an increased health risk, but no ongoing illness. This will facilitate a rational allocation of healthcare resources and a fair and medically meaningful prioritisation of available treatment options.”
Key findings in detail
There is an ongoing debate among clinicians and policymakers over the definition of obesity as a disease.
- A blanket definition in which everyone with obesity is considered as having a disease raises concerns that this can result in overdiagnosis, leading to unwarranted use of drugs, medical technologies, and surgical procedures, with potential harm for the individual and staggering costs for society.
- On the other hand, considering obesity only as a risk factor, and never a disease, can unfairly deny access to time-sensitive care among many people who are experiencing ill health due to obesity alone.
Obesity is currently defined by body mass index (BMI). A BMI at or above 30 Kg/m2 is considered as an indicator of obesity for people of European descent. Different, country-specific BMI cutoffs are also used to account for ethnic variability of obesity-related risk.
Although BMI is useful for identifying individuals at increased risk of health issues, BMI is not a direct measure of fat, does not reflect its distribution around the body and does not provide information about health and illness at the individual level.
Relying on BMI alone can lead to under-diagnosis of people who are ill and over-diagnosis of people who currently do not have negative health consequences of obesity.
- Some people are more likely to store excess fat in and around their organs, such as the liver, and muscles – this is associated with a higher risk for heart and metabolic disease, such as diabetes, than when excess fat is stored just beneath the skin in other body areas. These people, however, do not always have a BMI above the obesity threshold, meaning their health problems can go unnoticed.
- Athletes and other people with greater muscle mass tend to have higher BMIs despite normal levels of body fat. Their BMI may therefore misclassify them as having obesity.
- Some people may have a high BMI and high body fat, but maintain normal organ and body functions, with no signs or symptoms of ongoing illness. Diagnosing such people as having a disease can lead to unnecessary treatments.
A nuanced definition of obesity and clinically relevant methods for its diagnosis are urgently needed.
Whilst recognising BMI as a useful screening tool to identify people with potential obesity, the Commission recommends moving away from diagnosing obesity based on BMI alone.
The authors recommend confirmation of excess fat mass (obesity) using one of the following methods:
- at least one measurement of body size (waist circumference, waist-to-hip ratio or waist-to-height ratio) in addition to BMI;
- at least two measurements of body size (waist circumference, waist-to-hip ratio or waist-to-height ratio) regardless of BMI;
- direct body fat measurement (such as by a bone density scan) regardless of BMI;
- in people with very high BMI (i.e. >40Kg/m2) obesity can be pragmatically assumed.
People with clinical obesity have a chronic disease with reduced tissue or organ function or substantial trouble completing standard day-to-day activities due to excess or unusual distribution of body fat. A diagnosis of clinical obesity requires one or both of the following main criteria:
A. Evidence of reduced organ or tissue function directly due to excess body fat. The Commission sets out 18 diagnostic criteria for clinical obesity in adults and 13 specific criteria for children & adolescents, including:
- Breathlessness caused by effects of obesity on the lungs;
- Obesity-induced heart failure;
- Knee or hip pain, with joint stiffness and reduced range of motion as a direct effect of excess body fat on the joints;
- Certain alterations of bones and joints in children and adolescents limiting movement;
- Other signs and symptoms caused by dysfunction of other organs including kidneys, upper airways, metabolic organs, nervous, urinary and reproductive systems and the lymph system in the lower limbs.
B: Substantial trouble with movement or day-to-day activities such as bathing, dressing, eating and continence, due to the impact of excess body fat.
- People living with pre-clinical obesity have excess body fat but no signs of reduced organ or tissue function directly due to obesity and can complete day-to-day activities unhindered. People with pre-clinical obesity therefore have no ongoing illness although they have a variable but generally increased risk of developing clinical obesity and other diseases such as type 2 diabetes, cardiovascular disease and some cancers.
People with clinical obesity should receive timely, evidence-based treatment, as indicated for individuals suffering from any other chronic illness. Treatment for clinical obesity should be aimed to fully regain or improve the body functions reduced by excess body fat.
- The type of treatment and management – lifestyle, medication, surgery, etc – for clinical obesity should be informed by individual risk: benefit assessments and discussion with the patient.
- Successful treatment and management of clinical obesity should be assessed by the improvement of signs and symptoms, rather than measures of weight loss alone.
People living with pre-clinical obesity are at risk for future diseases but do not have ongoing health complications due to excess body fat. Accordingly, the approach to their care should aim at risk-reduction. This may require just health counselling and monitoring over time, or active treatment if necessary to reduce substantially high levels of risk.
This nuanced approach to obesity, which pragmatically distinguishes between individuals who do not have ongoing illness, albeit they are at increased health risk, and people who already have ongoing disease, will enable personalised approaches to obesity prevention, management and treatment with more appropriate and cost-effective allocation of resources.
Health insurers worldwide often require evidence of other conditions associated with obesity (e.g. type 2 diabetes) to provide coverage of obesity therapies. As a distinct chronic illness itself, clinical obesity should not necessitate the presence of another disease to justify coverage.
Weight-based bias and stigma present major obstacles to effectively prevent, manage and treat obesity. The Commission authors believe that their objective, clinically relevant reframing of obesity can contribute to eradicating misconceptions that contribute to stigma. They also call for proper training of healthcare professionals and policymakers to address this important issue.