BMI Is an Awful Predictor of Early Death. We've Had a Better Option For Decades.

Yahoo

02-07-2025

The 'go-to' way many clinicians measure healthy weight may be deeply flawed, according to new research.
A population study from the University of Florida (UF) has found that BMI, or body mass index, is not the best option for predicting future health risks associated with weight – not by a long shot.
Another method, which directly measures body fat and has been around for decades, has now put BMI to shame. It's called a bioelectrical impedance analysis (BIA).
In a nationally representative analysis, those with high body fat levels, as measured by BIA, faced a 262 percent increased risk of death from heart disease compared to those with lower levels.
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Meanwhile, BMI scores, which simply compare a person's weight to their height, failed to turn up any significant association with mortality.
"Let's face it, the magnitude of risk this study shows is enormous," cardiologist Andrew Freeman, who was not involved in the study, told CNN's Sandee LaMotte.
"It's scary to think that we may have been using a surrogate – BMI – that may not have been all that accurate over the years."
BMI has long been used as a standard measure of obesity, endorsed by the United States Centers for Disease Control and Prevention (CDC), the National Institute of Health (NIH), the World Health Organization (WHO), the American Heart Association (AHA), and many more.
In recent years, however, researchers around the world have begun to question BMI measurements, which do not consider body build, age, gender, sex, race, or ethnicity differences. Some medical organizations have even advised doctors to deemphasize the use of BMI.
Health services researcher, Arch Mainous, and his colleagues at UF have now proposed a much-needed alternative, and it takes less than a minute to carry out. BIA is a direct measurement of body fat using a portable, inexpensive device.
The contraption works by sending a weak electric current into body tissue to determine muscle and fat composition. The technology has been commercially available since the 1980s, but only recently have modern fitness trackers and smartwatches begun to incorporate BIA sensors.
While these measurements are not perfect and are subject to variability, UF's nationally representative study suggests that this 25-year-old technology is more accurate as a health indicator than BMI.
Over the course of 15 years, researchers found that adults who had high body fat, as measured by BIA, were 78 percent more likely to die of any cause than those with lower body fat levels.
By contrast, higher BMI levels did not reveal any significant relationship with all-cause mortality.
"This study is a game-changer," says lead author Mainous. "This is the ultimate Coke versus Pepsi test. And BMI failed."
Sure, BMI is simple and easy to compute, but it comes with some serious limitations. People who are muscular, for instance, can sometimes be deemed overweight or obese. And on the flip side, those who have a normal BMI but elevated body fat percentages may be unaware that they may face added health risks, such as metabolic syndrome or type 2 diabetes.
Mainous and colleagues argue that BIA is a more accurate alternative, and the devices that measure it are inexpensive and compact enough to become a regular feature of medical clinics.
The UF team predicts that if their results are validated in larger and more diverse cohorts, "it is likely that measuring body fat percentage with BIA will become a standard of care".
"These data will drive better discussions in the doctor's office as well as public health initiatives with the goal of improving the health of all," the researchers conclude.
The study was published in the Annals of Family Medicine.
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