BMI a poor predictor of future health

A new University of Florida Health study shows that body mass index, or BMI — commonly used to measure obesity and health risk — fails in predicting the risk of future death, suggesting the calculation is deeply flawed.

The study, published today (June 24) in the Annals of Family Medicine, concludes that a direct measure of body fat using a relatively inexpensive device that notes the resistance of body tissue to a small electrical current is far more accurate.

This method, bioelectrical impedance analysis, is increasingly found in medical practices.

Individuals who have high body fat as measured directly by bioelectric impedance are 78% more likely to die of any cause than those with healthy body fat levels during the 15 years they were tracked, the study found. They are also about three-and-a-half times more likely to die of heart disease.

By contrast, BMI proved entirely unreliable. The study showed no statistically significant association with 15-year mortality risk from any cause, including heart disease, when BMI is used.

BMI and bioelectrical impedance data were analyzed in a way that removes the effects of age, race and income.

Researchers in the UF College of Medicine’s Department of Community Health and Family Medicine who conducted the study urged physicians to move away from BMI as the standard body composition measure.

The study’s authors likened their research to a test between two competing means of measuring body fat, much like a product comparison.

“This study is a game-changer,” said Arch Mainous, Ph.D., lead author of the study and a professor and vice chair of research in the department. “This is the ultimate Coke versus Pepsi test. And BMI failed.”

The study pulled data from the National Health and Nutrition Examination Survey, which is linked to the national death index. The analysis involved 4,252 people, a representative sample of the U.S. population.

The study’s senior author, Frank Orlando, M.D., medical director of UF Health Family Medicine – Springhill, said BMI’s use as a “vital sign” of health isn’t supported by good evidence.

“I’m a family physician, and on a regular basis, we’re faced with patients who have diabetes, heart disease, obesity and other conditions that are related to obesity,” said Orlando, an associate professor in the department.

“One of the routine measures we take alongside traditional vital signs is BMI. We use BMI to sort of screen for a person having an issue with their body composition, but it’s not accurate for everyone like vital signs are,” he added.

BMI is calculated using an individual’s height and weight — the formula is weight divided by height, squared. But the measure cannot distinguish between muscle and fat mass, only providing an indirect indication.