Global report urges more accurate definition of obesity than BMI

There is a risk too many people are being diagnosed as obese when “a more accurate” and “nuanced” definition is needed, a report from global experts says.

Doctors should consider the overall health of patients with excess fat, rather than just measuring their body mass index (BMI), it says.

Those with chronic illnesses caused by their weight should be diagnosed with ‘clinical obesity’ – but those with no health problems should be diagnosed with ‘pre-clinical obesity’.

More than a billion people are estimated to be living with obesity worldwide and prescription weight-loss drugs are in high demand.

The report, published in The Lancet Diabetes & Endocrinology journal, is supported by more than 50 medical experts around the world.

“Obesity is a spectrum,” says Prof Francesco Rubino, from King’s College London, who chaired the group.

“Some have it and manage to live a normal life, function normally.

“Others can’t walk well or breathe well, or are wheelchair bound with significant health issues.”

The report calls for a “reframing” of obesity to distinguish between patients with a disease and those who remain healthy, but at risk of disease in the future.

Currently, in many countries, obesity is defined as having a BMI over 30 – a measurement that estimates body fat based on height and weight.

Access to weight-loss drugs such as Wegovy and Mounjaro is often restricted to patients in this category.

In many parts of the UK, the NHS also requires people to have a weight-related health condition.

But BMI reveals nothing about a patient’s overall health, the report says, and fails to distinguish between muscle and body fat or account for the more dangerous fat around the waist and organs.

The experts argue for a new model that looks at signs of obesity affecting organs in the body – such as heart disease, breathlessness, type 2 diabetes or joint pain – and their damaging impact on daily life.

This indicates obesity has become a clinical disease and needs drug treatment.

Those with ‘pre-clinical obesity’, however, instead of drugs and surgery, should be offered weight-loss advice, counselling and monitoring to reduce the chances of health problems developing. Treatment may also be necessary.

“Obesity is a health risk – the difference is it’s also an illness for some,” Prof Rubino said.

Redefining it was sensible, he added, to understand the level of risk in a large population, instead of the current “blurry picture of obesity”.

Waist-height ratios or direct fat measurement, along with a detailed medical history, can give a much clearer picture than BMI, the report says.

Children’s obesity expert Prof Louise Baur, from the University of Sydney, who contributed to the report, said the new approach would allow adults and children with obesity “to receive more appropriate care”, while reducing the numbers being over-diagnosed and given unnecessary treatment.

At a time when drugs that reduce body weight by up to 20% are being prescribed on a large scale, the report says this “reframing” of obesity “is all the more relevant” because it “improves the accuracy of diagnosis”.

The Royal College of Physicians said the report laid a strong foundation “for treating obesity with the same medical rigour and compassion as other chronic illnesses”.

Distinguishing between pre-clinical and clinical obesity would be “a vital step forward” and “highlighted the need to identify and intervene early” while providing the right care to patients whose health was already severely affected, the college said.

But there are concerns that pressure on health budgets could mean less money for those in the ‘pre-obese’ category.

Prof Sir Jim Mann, co-director of the Edgar Diabetes and Obesity Research Centre, in Otago, New Zealand, said the emphasis was likely to be “on the needs of those who are defined as clinically obese” and the limited funding was “very likely” to be directed towards them.