Dramatic increase in American adults who meet a new definition of obesity: ‘This is astounding’

More than 100 million American adults are living with obesity - and that number is set to skyrocket with new criteria for diagnosing the chronic condition.

Doctors in Massachusetts said Wednesday that the definition of obesity should be expanded beyond a simple body mass index (BMI) measurement, to include how fat is distributed across the body.

By applying this new framework to a test group of more than 300,000 patients, researchers found that the number of obese people jumped from 40 percent to 70 percent. The doctors believe that this statistic would be reflected across the U.S. population, meaning that one in four people would be considered obese.

BMI, first introduced in the 19th century, is an imprecise tool for assessing health risks, say the medical experts from Harvard and Mass General Brigham. Under the new, widely-endorsed framework, many more people could be considered for treatment for potentially life-threatening conditions like diabetes, cardiovascular disease, and certain cancers.

“We have always recognized the limitations of BMI as a single marker for obesity because it doesn't take into account body fat distribution,” Steven Grinspoon, Chief of the Metabolism Unit in the Endocrinology Division of the Mass General Brigham Department of Medicine, explained in a statement.

“We already thought we had an obesity epidemic, but this is astounding,” Dr. Lindsay Fourman, an endocrinologist in the Endocrinology Division of the Mass General Brigham Department of Medicine, added.

BMI is a calculated measure of a person's body weight divided by their height and has been increasingly scrutinized. During last year’s Summer Olympics, U.S. rugby star Ilona Maher made waves when she said that her BMI is technically listed as overweight, despite being one of the world’s top athletes.

“I am considered overweight. But alas, I’m going to the Olympics, and you’re not,” the Bronze medalist posted on TikTok.

Under the new framework, people would be classified obese with a high BMI and at least one other abnormal factor, such as a high waist circumference or waist-to-hip ratio. They would also be classified as having obesity if they have a normal BMI and two of those abnormal factors.

When assessing the study’s participants using these standards, obesity affected nearly 80 percent of adults over 70, the doctors said. A previous tally, from the Centers for Disease Control and Prevention, found that 41.5 percent of adults over 60 were living with obesity.

“Identifying excess body fat is very important as we’re finding that even people with a normal BMI but with abdominal fat accumulation are at increased health risk,” Fourman said. “Body composition matters – it’s not just pounds on a scale.”

However, the doctors stressed that more research needs to be done to understand the causes and treatments for new cases of obesity as defined by their framework. The guidelines have been endorsed by 76 organizations, including the American Heart Association and The Obesity Society.

Obesity is linked to more than 40 diseases, stroke and cancer. Being overweight or obese was associated with nearly 1 in 5 deaths in the U.S. between 1986 and 2006, according to the American Society for Metabolic and Bariatric Surgery.

Rates of obesity have tripled over the past 60 years in the U.S., tied to higher alcohol consumption, ultra-processed foods and a more sedentary lifestyle.

By 2050, experts say as many as 260 million Americans will be overweight or obese without “immediate action” to reverse trends.