A New Method To Diagnose Obesity Is Better Than Using BMI Alone, Study Asserts

FRIDAY, Nov. 13, 2026 (HealthDay News) — Millions of folks might unexpectedly find out they have obesity — or don’t — if doctors start using a new way of diagnosing excess weight, a new study says.

The new diagnostic method combines body mass index (BMI) with other measurements like waist circumference and waist-to-height ratio, and outperforms relying on BMI alone, researchers reported Nov. 11 in the journal Nature.

As many as 9% of people could learn they have undiagnosed obesity using the new approach, researchers found.

Likewise, they said up to 3% of people considered obese by BMI alone might find they’ve been misclassified.

The new measurement can also distinguish clinical obesity — an active disease of excess fat harming the body — versus preclinical obesity, which is excess fat not actively harming someone's health, researchers said.

People with clinical obesity have a 69% higher risk of death, compared to a 19% higher risk among people with preclinical obesity, the study found.

“This study shows that up to a third of all cases of obesity are clinical obesity, an active disease that should be treated as such,” senior researcher Dr. Francesco Rubino, chair of metabolic and bariatric surgery at King’s College London, said in a news release.

The new study aimed to test a diagnostic framework proposed by a commission of the Lancet Diabetes & Endocrinology journal in January 2025.

The Lancet guidelines use a two-step process:

• First, excess body fat is detected using a combination of BMI, waist circumference, waist-to-height ratio and other measurements.

• Second, people with excess body fat undergo follow-up analysis to determine if they have clinical or pre-clinical obesity.

BMI has been criticized as an inadequate means of assessing the health risks posed by excess weight.

For example, a bodybuilder can have an obesity-level BMI due to their heavy muscle mass, because BMI doesn’t distinguish between fat and muscle.

To test the new framework, researchers analyzed health data from more than 844,000 adults in China, the U.K., the U.S. and Spain.

Results showed that between 23% and 31% of all obesity cases involved clinical obesity, and that as many as 1 in 10 people (11%) have clinical obesity. Clinical obesity was also linked to a substantially higher risk of death.

“Body mass index alone cannot tell us whether someone is already ill or at risk of illness, or what care they need, leaving people vulnerable to both undertreatment and overtreatment,” Rubino said. “The new definition makes personalized, proportionate care possible whereas a uniform BMI-based definition prevents it.”

The majority of people with preclinical obesity — 77% to 91% — did not progress to clinical obesity over a 10-year span, researchers said.

“Most people with preclinical obesity, but not all, remained free of clinical obesity for a decade,” Rubino said. “Preclinical obesity should therefore be neither treated automatically as active disease nor dismissed as harmless. Some people may need preventive treatment, but its intensity should match their individual risk.”

Obesity treatment starts with a correct diagnosis, researchers pointed out. 

“Rapid advances in treatment make a clinically meaningful diagnosis increasingly important to guide proportionate care,” lead researcher An Pan, a professor at Huazhong University of Science and Technology in Wuhan, China, said in a news release.

Accurately parsing patients with clinical versus preclinical obesity will also become more important as medical science comes up with better ways to treat weight-related health problems, researchers said. 

“The marked differences in prognosis between clinical and preclinical obesity, consistently observed across countries and ethnic groups, support global adoption of the new framework to improve obesity care and policy worldwide,” Pan said.

More information

Northwestern University has more on the Lancet measure of obesity versus BMI.

SOURCE: King’s College London, news release, Nov. 11, 2026