Obesity needs a new definition, says global commission

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Obesity Action Coalition

The current approach to diagnosing obesity based on body mass index (BMI) is not fit for purpose as a marker for health – and by extension decisions on prescribing weight-loss therapies.

That is the conclusion of a report by the global Commission on Clinical Obesity – published in The Lancet Diabetes and Endocrinology – which recommends a more nuanced approach that includes BMI as well as other measures, including waist circumference or direct fat measurement.

That could help overcome problems with relying on BMI alone, which can't identify people who tend to store more 'visceral' fat in and around their organs, making them much more at risk of health issues than those who store it mainly under the skin.

Meanwhile, some people with a normal-range BMI may also have visceral fat and be considered 'metabolically obese', but fall under the threshold for intervention.

The Commission proposes a new system in which people with chronic health problems resulting from excess weight are classed as having clinical obesity, while those with no health problems would be considered to have preclinical obesity.

That view aims to defuse the highly polarised debate about whether obesity itself is a disease or not, a binary view that Commission chair Professor Francesco Rubino of King's College London (KCL) describes as "flawed", given that some people with obesity remain healthy, even in the long term, while others can quickly develop severe illnesses.

"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," according to Prof Rubino.

"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."

With more than a billion people worldwide coming under the current obesity definition, there is a massive demand for newer weight-loss medicines, such as Novo Nordisk's Wegovy (semaglutide) and Eli Lilly's Zepbound (tirzepatide), and concern that widespread use could place massive pressure on health system budgets.

In the UK, for example, NHS use of these drugs is currently restricted to people with a BMI of 30 or more and a weight-related health condition like diabetes or cardiovascular disease.

Using the new definition, weight-loss drugs or other interventions like surgery would be considered for those with clinical obesity, while those with preclinical obesity would be offered other measures like weight-loss guidance and health monitoring.

The approach allows for "personalised care" that will "facilitate a rational allocation of healthcare resources and a fair and medically meaningful prioritisation of available treatment options," according to Prof Rubino.

That view was echoed by Prof Tom Sanders, Emeritus Professor of Nutrition and Dietetics at KCL, who said the recommendations are helpful because they will help target interventions to those that need them most.

"The recognition of clinical obesity as disease would hopefully persuade lawmakers to regard it as a disability," he added. "This would have implications in terms of discrimination, particularly in employment, as well as the social stigma associated with the condition."

The Commission's report was prepared by 56 international medical experts and is endorsed by more than 75 medical organisations around the world.