Beyond BMI: Scientists propose a new way to define obesity: Shots

An international committee of scientists has proposed changing the way obesity is defined and diagnosed. The goal is to offer a more nuanced and objective way to assess body composition, by adding more measurements, such as waist circumference, to the criteria.

For years, the method doctors have used to determine if a person is obese has been to calculate their BMI – or body mass index. BMI is a quick and inexpensive estimate based on weight and height.

But BMI does not provide adequate information about a person’s health, the commission concludes, and relying on BMI alone can lead to misdiagnosis.

The current measure of obesity based on BMI can both overestimate and underestimate the amount of body fat a person has, says Dr. Robert Kushner, an endocrinologist at Northwestern University who is on the Commission on Diabetes and Endocrinology from the Lancet.

“Approximately 40% of the U.S. adult population suffers from obesity, even though it is defined solely by BMI,” says Kushner. But do all of these millions of Americans suffer from a disease? And do they all need treatment? Kushner says the commission aims to clarify the confusion.

Some people are stocky and muscular. When they step on the scale, their body weight can put them in the obese category, due to the weight of muscle mass. But these people may be healthy.

On the other side of the coin, some people have very low muscle mass, but carry excess weight around their organs. Their BMI may be normal, but their abdominal fat level may put them at risk for metabolic disease.

“What’s new is we’re trying to define obesity by excess body fat, which is what obesity actually is,” Kushner says.

The commission recommends that excess body fat should be confirmed by measuring a person’s waist circumference, waist-to-hip ratio, or waist-to-height ratio. Another option is a direct measurement of body fat from a screening, such as a DEXA scan, when this option is available and affordable.

“We’re not dismissing BMI, we’re now recommending that individuals get another measurement that more directly gives an estimate of body fat,” says Kushner.

Bottom line: The new measurements focus on how much fat people carry around their waists.

“Belly fat causes systemic inflammation, which then continues and causes other metabolic problems like high blood sugar, high blood pressure, and increased fats in the blood,” says Kushner. This can pave the way for metabolic diseases, including diabetes, as well as heart disease.

Additionally, the commission recommends two new categories of obesity, based on objective measures of the disease. The first category is called “clinical obesity,” for people who already have a chronic illness associated with obesity. And the second category is called “preclinical obesity” and would mean that a person is at high risks of developing a health problem due to their body fat level.

“Our reframing recognizes the nuanced reality of obesity and enables personalized care,” says Dr Francesco Rubino, of King’s College London, who chairs the commission.

The Commission included 56 experts with expertise in nutrition, endocrinology, internal medicine and public health. Their report is published in the Newspaper Lancet Diabetes and endocrinology.

The report comes amid a significant increase in obesity worldwide. The World Health Organization estimates that more than a billion people live with obesity, and the World Obesity Federation estimates that the economic impact of the disease will exceed $4 trillion by 2035 .

This story was edited by Jane Greenhalgh