By Dr Joe Milton, the Australian Science Media Centre
The accepted medical definition of obesity, which is based on measuring body mass index (BMI) alone, is an oversimplification that fails to distinguish between excess weight which is causing ongoing health problems, and excess weight which is not currently causing such issues, according to a major international report launched this week at an AusSMC Briefing.
The report from the Global Commission on Clinical Obesity recommends splitting obesity into two distinct categories: clinical obesity - when excess weight is causing ongoing health problems - and pre-clinical obesity - when excess weight is not yet causing ongoing health problems.
Body mass index (BMI) is a simple weight-to-height ratio, and is not a reliable indicator of clinical obesity, the report's authors told journalists at the briefing.
“It doesn’t compute the body composition,…doesn’t tell us how well our organs are working, if they’re still normal or they’re dysfunctional, and therefore whether there is health or illness at the individual level,” Commission Chair Professor Francesco Rubino of King's College London, UK, told journalists at the briefing.
Instead, he said, doctors should consider other body fat measures and signs and symptoms of ill health when diagnosing the condition.
The report proposes 18 diagnostic criteria, taking a range of health problems, from sleep apnoea to liver disease, into account.
The idea was "to overhaul, dramatically, the ideas about how we diagnose obesity and how we improve global health care practices”, said Adjunct Professor John Dixon from Swinburne University, another author of the report.
Prof Rubino said new criteria are needed because "obesity is a spectrum".
"You can have people who have excess body fat but have preserved normal organ function, and can go about their lives for quite some time in a normal way, sometimes even for a lifetime,” he said.
Failing to distinguish between types of obesity can lead to preclinical obesity being diagnosed as clinical obesity, he warned. And our current, oversimplified approach can potentially lead to people with either category of obesity missing out on the most effective treatments and approaches.
"We cannot afford to not treat clinical obesity, but cannot afford over-diagnosis of obesity," said Prof Rubino.
“If somebody has already developed clinical obesity, that person has a disease here and now…and it would be inappropriate if we were using preventative or prophylactic interventions to treat an ongoing disease,” he added.
The University of Sydney's Professor Louise Baur, a former World Obesity Federation chair and an author of the report, said the new guidelines "acknowledge the nuanced reality" of obesity. However, it's not the end of the road for BMI, she added: "We don't want to throw out BMI but we want it to be used in a thoughtful way."
That would involve continuing to use BMI as a screening tool, but in combination with waist measurements, waist-to-hip ratios, waist-to-height ratios, or body fat scans.
The University of Sydney's Honorary Professor Tim Gill, Director of The Obesity Collective, who was not involved in the report, told the AusSMC he thinks the new guidelines will help address the issues around over- and underdiagnosis of clinical obesity.
"These new criteria will not only help avoid the misclassification of overwise healthy people living in a larger body as obese, but will also help better target the limited healthcare resources and services to those individuals most in need of immediate care," he said.
“The aim is to…deliver the right services to the right people,” concluded A/Prof Dixon.
You can read about the briefing and Expert Reaction here
This article originally appeared in Science Deadline, a weekly newsletter from the AusSMC. You are free to republish this story, in full, with appropriate credit.
Contact: Joe Milton
Phone: +61 8 7120 8666
Email: info@smc.org.au