An international committee of experts has urged doctors to move away from relying on BMI in diagnosing obesity to take a more personalised approach to an individual’s actual health risk.
A ‘radical overhaul’ that takes into account measures of body fat is needed to avoid both under and overdiagnosis of obesity, a Lancet Commission concluded.
Current guidelines which rely heavily on BMI can prevent people accessing evidence-based treatments from which they would benefit, they added.
The panel of 50 specialists, led by UK clinicians, also called for two new diagnostic categories of obesity.
Clinical obesity should be defined as a ‘chronic systematic illness’ where excess fat can lead to organ damage and cause ‘life-altering and potentially life-threatening complications’.
Those with clinical obesity may have breathlessness, joint pain or other metabolic conditions or diseases.
By contrast they suggested that pre-clinical obesity is a condition of obesity with normal organ function.
Those affected have variable and generally increased risk of developing conditions in the future such as type 2 diabetes, cardiovascular disease and certain types of cancer.
The commission published in The Lancet Diabetes & Endocrinology recommended several options other than BMI for measuring excess fat mass and its distribution around the body.
This could be:
- At least one measurement of body size (waist circumference, waist-to-hip ratio or waist-to-height ratio) in addition to BMI
- At least two measurements of body size (waist circumference, waist-to-hip ratio or waist-to-height ratio) regardless of BMI
- Direct body fat measurement using a scan regardless of BMI
But in people with very high BMI, for example more than 40 Kg/m2, excess body fat can be pragmatically assumed, the panel said.
Commission chair, Professor Francesco Rubino, chair of metabolic and bariatric surgery at King’s College London, said: ‘The question of whether obesity is a disease is flawed because it presumes an implausible all-or-nothing scenario where obesity is either always a disease or never a disease.
‘Evidence, however, shows a more nuanced reality. Some individuals with obesity can maintain normal organs’ function and overall health, even long term, whereas others display signs and symptoms of severe illness here and now.’
He added: ‘Considering obesity only as a risk factor, and never a disease, can unfairly deny access to time-sensitive care among people who are experiencing ill health due to obesity alone.
‘On the other hand, a blanket definition of obesity as a disease can result in overdiagnosis and unwarranted use of medications and surgical procedures, with potential harm to the individual and staggering costs for society.’
NICE does recommend GPs measure waist to height ratio in people with a BMI under 35 kg/m2 but referral to specialist services and access to treatment on the NHS is based on BMI cut-offs with some consideration of other co-morbidities.
The NHS has adopted a slow roll-out of weight loss drugs because the numbers who would be eligible would have a ‘profound impact’ on GPs.
The Royal College of Physicians endorsed the approach set out by the commission.
Dr Kath McCullough, RCP special adviser on obesity, said: ‘For too long, we’ve relied on BMI as a simple measure of obesity, which has often misrepresented the condition and fails to fully reflect how excess body fat impacts a person’s health.
‘The commission’s distinction between pre-clinical and clinical obesity represents a vital step forward, highlighting the need to identify and intervene early while providing appropriate care to those already experiencing severe health impacts.’
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