According to the recommendations published Tuesday evening, obesity would no longer be defined solely by BMI, a calculation of height and weight, but combined with other measurements, such as waist circumference, as well as evidence health problems linked to excess weight.
Obesity is estimated to affect more than a billion people worldwide. In the United States, about 40 percent of adults suffer from obesity, according to the U.S. Centers for Disease Control and Prevention.
“The goal is to get a more precise definition to target the people who need help the most,” said Dr. David Cummings, an obesity specialist at the University of Washington and one of the 58 authors of the report published in the journal The Lancet Diabetes & Endocrinology.
The report introduces two new diagnostic categories: clinical obesity and preclinical obesity.
People with clinical obesity have lower BMI and other markers of obesity, as well as signs of organ, tissue, or other problems caused by excess weight. This could include heart disease, high blood pressure, liver or kidney disease, or severe chronic knee or hip pain. These people may benefit from treatments including diet and exercise interventions and anti-obesity medications.
People with preclinical obesity are at risk for these conditions but do not have an ongoing disease, the report said.
BMI has long been considered an imperfect measure that can overdiagnose or underdiagnose obesity, currently defined as a BMI of 30 or greater. But people with excess body fat don’t always have a BMI over 30, the report notes. Additionally, people with high muscle mass – football players or other athletes – may have a high BMI despite having normal body fat.
Under the new criteria, about 20% of people who were classified as obese would no longer meet the definition, according to preliminary analysis. Furthermore, around 20% of people with serious health effects but a lower BMI would now be considered clinically obese, according to experts.
“It wouldn’t dramatically change the percentage of people defined as obese, but it would make it easier to diagnose people who actually have clinically significant excess fat,” Cummings said.
The new definitions have been endorsed by more than 75 medical organizations around the world, but it is unclear whether they can be adopted quickly or widely in practice. The report acknowledges that implementing the recommendations “will result in significant costs and impact on the workforce.”
A spokesperson for AHIP, the health insurance trade association, formerly known as America’s Health Insurance Plans, said that “it is still too early to know how plans will incorporate these criteria into coverage or in other policies.”
There are practical issues to consider, according to Dr. Katherine Saunders, an obesity specialist at Weill Cornell Medicine and co-founder of the obesity treatment company FlyteHealth. Measuring waist circumference seems simple, but protocols differ, many doctors are not accurately trained, and standard medical tape measures are not large enough for many people with obesity.
Additionally, determining the difference between clinical and preclinical obesity would require a comprehensive health assessment and laboratory tests, she noted.
“For a new classification system to be widely adopted, it would need to be extremely fast, inexpensive and reliable,” she added.
According to Kate Bauer, a nutrition expert at the University of Michigan School of Public Health, the new definitions are likely to cause confusion.
“The public likes simple messages and needs them. I don’t think this differentiation will change anything,” she said.
Revising the definition of obesity will take time, acknowledged Dr. Robert Kushner, an obesity specialist at the Northwestern Feinberg School of Medicine and co-author of the report.
“This is the first step in the process,” he said. “I think it will help start the conversation.”
