New Obesity Benchmark Adds Body Fat, Organ Health to BMI

The recommendation signals a long-awaited shift from a single imperfect metric toward a more personalized diagnosis that takes into account a person’s ability to accomplish everyday tasks and the state of their organs. It may also limit the prescription of blockbuster weight-loss drugs.

The Lancet Diabetes and Endocrinology Commission, consisting of experts from around the world, put forward the new definition for obesity on Tuesday. It was endorsed by 76 organizations including the World Obesity Federation, the American Heart Association and Britain’s Royal College of Physicians. 

“The commission is re-framing obesity and acknowledges the nuanced reality of obesity,” said Robert Eckel, emeritus professor of medicine at the University of Colorado Anschutz Medical Campus and one of the group’s members. 

The body mass index, a weight-to-height ratio, has long been criticized as too simplistic, in part because it can’t distinguish between fat and muscle mass. Currently, anyone with a BMI of 30 or more is considered obese, regardless of their body composition or general fitness. 

A new generation of obesity drugs like Novo Nordisk A/S’s Wegovy and Eli Lilly & Co’s Zepbound is changing the perception of obesity as a multi-faceted illness that requires medical intervention rather than greater willpower, ushering a revolution with ripple effects from food manufacturing to medical insurance. 

BMI is more useful on a population level rather than an individual one, according to Francesco Rubino, commission chair and head of metabolic and bariatric surgery at King’s College London. 

“BMI contains no information about the functioning of organs,” he said. “For instance, how well is the heart functioning? Are the lungs doing their job as normal?”   

Under the new guidelines, patients whose BMI previously classed them as obese should get checked for excess fat with tools such as waist circumference or waist-to-hip ratio. If they have excess fat, the doctor should look for signs of organ dysfunction or limitations in day-to-day activities.

A person will only be considered as clinically obese if those last measurements are also positive. Otherwise they will be classed as having pre-clinical obesity. 

The new benchmark should be included in clinical-practice guidelines and in the training of health-care workers, according to the Lancet commission. It applies to adults regardless of age, gender or ethnicity, said the University of Colorado’s Eckel. 

The new framework could help clinicians determine whether a patient needs medicines or just monitoring and general health advice. It may also, as a result, impact how obesity drugs are prescribed. 

Wegovy and Zepbound are approved in the US for anyone with a BMI of 30 or more. The threshold is 27 for individuals with a weight-related condition like high blood pressure or sleep apnea. But under a new set of rules, some patients who were previously considered obese may no longer qualify for the treatments. 

Drugmakers are also increasingly looking at the importance of body composition, with companies trying to create therapies that help people keep muscle even as they shed fat. 

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