The longtime reliance on BMI means that obesity is likely overdiagnosed, members of the Commission said.
The way obesity is diagnosed needs a “radical overhaul,” according to a group of global health experts who called for a more objective, nuanced approach to one of the world’s most common health conditions.
About one in eight people are living with obesity worldwide, and it is a risk factor for many health issues, including type 2 diabetes, cardiovascular disease, certain cancers, and chronic respiratory diseases.
But obesity can also be a disease on its own, marked by reduced organ function or difficulty with daily activities as a direct result of excess body fat, according to the expert group, which included 56 leading specialists and patients who first convened in 2019 and published their findings in the Lancet Diabetes & Endocrinology medical journal.
However, not everyone with obesity is actually sick, the group said, making it important to distinguish between two categories: clinical obesity, which is an ongoing chronic disease, and preclinical obesity, which is when someone is obese and at higher risk of other health issues, but has normal organ function.
“There are some people who have obesity and manage to live a relatively normal life … and on the other hand you have [people] who may suffer significant health issues due to obesity alone,” Dr Francesco Rubino, the Lancet Commission’s chair and chair of metabolic and bariatric surgery at King’s College London, told reporters during a press briefing.
The new approach, Rubino said, will “give us a more accurate way of reflecting the problem than if we go with a blanket definition of [obesity as] a health risk only or as a disease only”.
The problem with BMI
Currently, doctors diagnose obesity mainly based on a patient’s body mass index (BMI), which is calculated using their weight and height.
Adults with a BMI of at least 30 are considered obese.
BMI has been used widely since the 1990s after the World Health Organization (WHO) started using it as an official obesity screening measure. It is correlated to body fat percentage and related health risks, making it a simple proxy.
But a growing chorus of physicians, researchers, and activists have been pushing to retire BMI in recent years, and in 2023, the US’s largest doctors’ group recommended that it be de-emphasised as it is an “imperfect clinical measure”.
Key among the problems is that BMI doesn’t directly measure fat mass or how it is distributed around the body and the organs, which influences health risks.
“It’s not just how much fat you have, it’s also where the fat is that’s important,” Dr Adam Collins, an associate professor of nutrition at the University of Surrey in the UK who was not involved with the commission, told Euronews Health.
People with very different body types can also wind up with the same BMI – including some who may not be obese at all, such as athletes with high muscle mass, the Lancet Commission noted.
“You’re not going to be able to put loads of people in an MRI as a routine measure,” Collins said.
“But you need to have some other marker of health that goes alongside that BMI to see what the implications of that BMI are”.
A new way to think about obesity
Following the new standards, which were endorsed by more than 75 medical groups worldwide, doctors would still use BMI as a screening tool.
But the official diagnosis of clinical obesity would rely on 18 criteria for adults and 13 for children and adolescents, including obesity-induced breathlessness, heart failure, knee or hip pain, and other signs of organ dysfunction.
Rubino and other experts said the current focus on BMI means that obesity is likely being overdiagnosed, but it isn’t clear by how much.
The new approach, they said, could help ensure patients across the obesity spectrum receive medical care based on their own health needs and level of risk, rather than focusing on weight loss alone.
“Whatever kind of treatment we use, whether it’s lifestyle, surgery, or drugs, will have to be” tailored to the individual patient, Rubino said.
Collins noted that could be particularly important when it comes to prioritising access to expensive weight-loss drugs such as Wegovy and Mounjaro.
Governments across Europe have been grappling with whether and how to pay for the drugs, given the potential hit on their budgets.
“It’s very costly and there’s not much of it around. It’s a scarce supply,” Collins said. “You need to target it to people where it’s going to have the biggest impact or the biggest need”.
It will take time before the diagnostic changes are apparent in doctors’ offices, Collins said, but the recommendations could help put metabolic health on the radar for people of all sizes, as well as combat the “massive” social stigma around obesity.
Rubino agreed saying he hoped “this leads to a change in practice and maybe even before that, a change in mindsets”.
