Experts weigh in on ‘flawed’ BMI as global report says obesity needs new definition
by Bethan Finighan · Manchester Evening NewsExperts are proposing a new way to define obesity, calling for an overhaul on the controversial body mass index (BMI). Medics warn people are being “overdiagnosed” with obesity because the BMI score is not a “nuanced” enough measure of the condition.
A new global report claims using BMI as a sole measure of obesity can lead to both overestimates and underestimates of the number of people living with obesity.
The new Lancet Commission – made up of more than 50 experts from around the world – said that a “radical overhaul” is needed in the diagnosis of obesity. Under the proposed diagnostic criteria, roughly 20% of people currently classified as obese would no longer meet the definition, preliminary analysis suggests.
“Some people who are today classified as having obesity by BMI (but) they might play sports, they’re very active, they might have very strong bones – saying that those people have obesity and then classifying them as having a disease would obviously be an overdiagnosis,” said Professor Francesco Rubino, chairman of the commission and chairman of metabolic and bariatric surgery at King’s College London.
“This commission has been trying to deal with a more accurate way of diagnosing and classifying obesity in the first place.
“But we are calling for a change, a radical change, because obviously, in the context of one billion people being classified as having obesity in the world today, and with a number that is projected to increase, no country is rich enough to be able to afford inaccuracy in the diagnosis of obesity.”
(Image: PA)
The authors propose that other measures should be taken to diagnose obesity, such as waist to hip ratio or waist to height ratio, and called for two new “diagnostic categories” of obesity. These are:
- Clinical obesity – defined as a “chronic systematic illness” whereby excess fat can lead to organ damage and cause “life-altering and potentially life-threatening complications”.
- Pre-clinical obesity - a “state of excess adiposity” where the person has a variable level of health risk, but no ongoing illnesS
Medical experts have reacted to the proposed major overhaul of obesity diagnosis. Prof Simon Griffin, Professor of General Practice, MRC Epidemiology Unit, University of Cambridge, questioned whether “there is a danger of the baby being thrown out with the bathwater.”
“While there are limitations with BMI, a problem with waist and hip circumference is that they are rarely measured in primary care, patients tend not to like having them done and they are time-consuming to assess accurately,” says Prof Griffin.
“The anticipated improved prediction of ‘disease’ through measurement of waist is unlikely to be realised as waist will be imprecisely measured in primary care, although accuracy can be improved with pictorial instructions.
“For the vast majority of the population BMI works reasonably well. Furthermore, it is better to have some data than none. If someone tells me their weight and height the resultant BMI calculation is usually not too far from the truth.”
Prof Griffin also highlighted that there was no department of general practice or primary care listed in the institutional affiliations of the 58 academics who worked on the study, claiming it is “unrealistic to expect practitioners to (re)measure 65% of the adult population” living with obesity.
One expert even warned the proposed diagnostic criteria could result in “metabolically obese” people – who often have a normal BMI – being overlooked.
“It is also important to note that focusing solely on BMI as a marker of health, even with this suggested differential diagnosis, does miss other individuals who may be at risk despite a normal BMI,” explains Dr Adam Collins, Associate Professor of Nutrition, University of Surrey.
“Those who can be described as “metabolically obese”, and who exhibit similar or greater metabolic risk than those who are obese. This may represent up to 1 in 10 “lean” individuals who would otherwise go undetected, emphasising the need for more routine measures of risk, than simply BMI, to identify individuals at risk.”
Others, however, have welcomed the findings of the global report. Dr Laura McGowan, Senior Lecturer in Nutrition and Behaviour Change, Queen’s University Belfast, branded it “an important step forward in the field of obesity.”
““It advances scientific agreement across a broad range of experts on what constitutes clinical obesity, and how we can consider this as a clinical condition in its own right, and more than just a risk factor for other conditions, like type 2 diabetes and cardiovascular disease.
“The research is robust in its methods and a strength is that it included the views and opinions of those living with obesity.”