Obesity should be divided into two groups, says a global report

Calling people obese is medically “wrong” – and the definition should be split into two, report of world experts says.

The term “clinical obesity” should be used for patients with a medical condition caused by their weight, while “preclinical obesity” should be applied to those who remain fat but fit despite being at risk of disease.

And it’s better for patients than relying solely on body mass index (BMI) — which measures whether they’re a healthy weight for their height — to determine obesity.

It is estimated that there are more than a billion people 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 worldwide.

“Some obese people can maintain normal organ function and overall health, even in the long term, while others show signs and symptoms of severe disease here and now,” said Prof. Francesco Rubino of King’s College London, who chairs the expert group.

“Obesity is a spectrum,” he added.

The current common definition means too many people are being diagnosed as obese but not receiving the most appropriate care, the report said.

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

It is calculated by dividing an adult’s weight in kilograms by their height in meters squared.

For example, if they are 70kg (about 11 stone) and 1.70m (about 5ft 7in):

• square their height in meters: 1.70 x 1.70 = 2.89
• divide their weight in kilograms by this sum: 70 ÷ 2.89 = 24.22
• display the result to one decimal place: 24.2

Find out what your body mass index (BMI) means on the NHS website

But BMI has limitations.

It measures whether someone is carrying too much weight — but not too much fat.

So very muscular people, like athletes, usually have a high BMI but not a lot of fat.

The report says BMI is useful on a large scale to determine what proportion of the population is at a healthy weight, overweight or obese.

But it reveals nothing about an individual patient’s overall health, whether they have heart problems or other illnesses, for example, and fails to differentiate between different types of body fat or measure the more dangerous fat around the waist and organs.

Measuring a patient’s waist or body fat, along with a detailed medical history, can give a much clearer picture than BMI, the report said.

“Obesity is a health risk – the difference is that for some it is also a disease,” said Prof. Ruby.

Clinical obesity

When obesity is a disease, there will be signs that it affects the organs in the body – through heart disease, shortness of breath, type 2 diabetes or joint pain – and a person’s daily activities. It is likely to be treated with drugs or surgery.

Preclinical obesity

When obesity is a health risk – but not yet causing any disease – people should be offered weight loss advice, counseling and monitoring to reduce the chances of developing health problems.

Doctors should also pay close attention to a patient’s family history to see if they are at risk for certain diseases.

At a time when drugs that reduce body weight by up to 20% are being prescribed on a large scale, the report says that redefining obesity “is even more urgent” as it “improves the accuracy of diagnosis”.

Access to weight loss drugs such as Wegovy and Mounjaro is often limited to patients with a BMI over 30 and a weight-related health condition.

The expert on childhood obesity prof. Louise Baur of the University of Sydney, who contributed to the report, said the new approach would allow obese adults and children to “receive more appropriate care” while reducing the number of people overdiagnosed and receiving unnecessary treatment.

The Royal College of Physicians said the report laid a strong foundation “for obesity to be treated with the same medical rigor and compassion as other chronic diseases”.

But others worry that the pressure on health budgets could mean less money for patients in the “pre-obese” category.