Only between a quarter and a third of people now diagnosed with obesity should be counted as in poor health, according to a new study that adds weight to calls to overhaul obesity diagnosis. The study, published in Nature on Wednesday, tested a new framework that looks beyond body mass index, or BMI, to decide who is ill and who is mainly at risk.
The study used data from 844,108 adults in China, Britain, the United States and Spain. The study drew on four large groups of adults in those countries and followed how the two groups fared over time. Under the new framework for obesity diagnosis, only about 27 percent of people with obesity across the four countries had clinical obesity, or about 8.5 percent of all adults in the study.
Obesity diagnosis split into two groups
The new obesity diagnosis framework splits obesity into two groups. Pre-clinical obesity is when excess body fat is largely a risk factor, with the body’s organs still working as they should. Clinical obesity is when excess fat is causing ill health, by impairing how organs work or limiting daily activities.
The proposal came last year from a Lancet Commission of experts and medical organizations, published in The Lancet Diabetes and Endocrinology. The new study, by An Pan and colleagues, set out to test what the framework would mean in practice for diagnosis levels, prevalence and treatment.
Under the new approach to obesity diagnosis, a diagnosis rests on more than weight and height. It calls for measuring body fat, including waist circumference, as well as BMI, and checking whether a patient has organ trouble linked to weight, such as heart or liver problems, before a diagnosis is made.
Obesity diagnosis and the limits of BMI
BMI, a measure based on a person’s weight and height, has long been the main tool for defining obesity. The study’s senior author, Francesco Rubino, professor and chair of metabolic and bariatric surgery at King’s College London, said the inaccuracy of BMI measurements was well known. BMI has been the standard measure for decades, and the study tested whether adding waist size and organ checks would do better. It found that they did, in all four groups studied.
Using data from the four groups, the study estimated that 1 percent to 3 percent of people defined as obese using BMI alone would not be counted as obese under the new framework. Under the new framework, obesity diagnosis would change for another 5 percent to 9 percent of people, including those with higher body fat, who would be diagnosed with the condition for the first time.
The four groups in the study were the Kailuan Study in China, with 137,795 people; the UK Biobank, with 436,203; the All of Us Research Program in the United States, with 218,841; and the SIDIAP database in Spain, with 51,269. The framework also recommends waist-to-height ratio or fat measurement with dual-energy X-ray absorptiometry, where available, to confirm excess body fat.
Obesity diagnosis and the risk of death
The new obesity diagnosis framework did better than BMI alone at diagnosing obesity and at sorting people by their risk of death, the Nature summary said. The World Health Organization estimates that obesity affects more than one billion people around the world, and it can raise the risk of type 2 diabetes, cardiovascular disease, liver and kidney disease and cancer.
Under the framework, obesity is confirmed in one of three ways: a BMI of 40 or higher; a BMI of 30 or higher together with a large waist or a high waist-to-height ratio; or a BMI between 25 and 29.9 together with both a large waist and a high waist-to-height ratio. A large waist was set at 102 cm or more for men and 88 cm or more for women, with lower cut-offs for Chinese adults. The paper, “Validation of clinical and preclinical obesity across global cohorts,” was published in Nature on 11 November, in volume 653, pages 510 to 518. Its summary said the framework outperformed conventional BMI-based criteria in diagnosing obesity and in sorting people by mortality risk.