• Posted June 27, 2025

Body Fat Analysis, Waist Size Better Than BMI For Assessing Health

A person’s body fat percentage provides a better estimate of their risk for early death than their body mass index (BMI), a new study says.

People with a high body-fat percentage were 78% more likely to die within 15 years from any cause and 3.6 times more likely to die from heart disease, researchers reported June 24 in the Annals of Family Medicine.

On the other hand, BMI — an estimate of body fat based on height and weight — was not associated with a statistically significant higher risk of death from any cause, researchers found.

Waist circumference also proved to be more accurate than BMI in assessing the risks posed by excess weight, researchers added.

"This is a game changer for body composition assessment,” lead researcher Arch Mainous III, a professor of health services, management and policy at the University of Florida, said in a news release.

“Our study is basically a Coke versus Pepsi comparison of a direct and indirect measure of body fat for future mortality risk,” Mainous said. “A direct measure of body fat percentage that can be done in the office was significantly better.”

The new findings add to mounting evidence that BMI is not as accurate as other measures for reflecting the effect of a person’s weight on their health.

"The medical community has been aware that BMI has some limitations as a measure of body composition and disease risk. It is an indirect measure of body fat percentage,” senior researcher Dr. Frank Orlando, an associate professor of community health and family medicine at the University of Florida, said in a news release.

BMI is calculated by dividing a person’s weight by their height. It’s a simple calculation, but leaves out some key distinctions, such as weight caused by fat versus muscle mass.

“For example, people who are bodybuilders can really elevate their body mass index,” Orlando said. “But they’re healthy even with a BMI indicating they’re obese.”

Up to now, doctors have made do with BMI because more direct measures of body fat have been too expensive and difficult for doctors and researchers to implement, Orlando said.

But newer devices that use bioelectric impedance analysis (BIA) to measure body fat are becoming increasingly cheaper and, thus, more commonly found in medical practices, researchers said.

These devices calculate a person’s body fat percentage based on the fact that fat-free body mass like muscle conducts electricity, while body fat doesn’t.

For the new study, researchers analyzed data on more than 4,200 people 20 to 49 who participated in the National Health and Nutrition Survey between 1999 and 2004.

All of the participants had their height, weight and waist circumference measured as part of the survey, and their body fat was assessed using BIA, researchers said.

The team compared these measures to death records running through 2019, to track each participant for 15 years.

Results show that body fat analysis did indeed predict people’s risk of death from any cause and, specifically, for heart disease, while BMI did not.

Men with 27% or more body fat and women with 44% or more were more likely to die within 15 years compared to those with less body fat, researchers found.

Waist circumference also proved another means of accurately predicting a person’s risk of death, researchers noted. 

People with high waist circumference — more than 40 inches in men and more than 35 in women —  were 59% more likely to die from any cause and 4 times more likely to die from heart disease.

“Our study shows that a direct measure of body fat that can be done easily, practically and inexpensively in a doctor's office solves the problems of BMI," Orlando concluded.

More information

Harvard T.H. Chan School of Public Health has more on body fat.

SOURCES: American Association of Family Physicians, news release, June 24, 2025; University of Florida, news release, June 24, 2025