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Body mass index (BMI) may not be the most accurate predictor of death risk.
A new study from the University of Florida found that BMI — a measurement that is commonly used to determine whether a person’s weight is in a healthy range for their height — is “deeply flawed” in terms of predicting mortality.
Instead, one’s level of body fat is “far more accurate,” concluded the study, which was published this week in the Annals of Family Medicine.
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To measure participants’ body fat, the researchers used a method called bioelectrical impedance analysis (BIA), which uses a device to measure the resistance of body tissue to a small electrical current.
Over a 15-year period, those who had high body fat were found to be 78% more likely to die than those who had healthy body fat levels, researchers found.
Body mass index (BMI) may not be the most accurate predictor of death risk, researchers say. (iStock)
They were also more than three times as likely to die of heart disease, the study noted.
BMI — which is calculated by dividing weight by height, squared — was described as “entirely unreliable” in predicting the risk of death over a 15-year period from any cause.
The study included 4,252 people in the U.S. and pulled data from the National Health and Nutrition Examination Survey.
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BMI should not be relied upon as a “vital sign” of health, according to senior author Frank Orlando, M.D., medical director of UF Health Family Medicine in Springhill.
“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,” Orlando said in a press release for the study.
Over a 15-year period, those who had high body fat were found to be 78% more likely to die than those who had healthy body fat levels, researchers found. (iStock)
“One of the routine measures we take alongside traditional vital signs is BMI. We use BMI to screen for a person having an issue with their body composition, but it’s not as accurate for everyone as vital signs are,” he added.
BMI has been the international standard for measuring obesity since the 1980s, according to many sources, though some experts have questioned its validity.
“I think the study shows it’s time to go to an alternative that is now proven to be far better at the job.”
An individual is considered obese if their BMI is 30 or above, overweight if it is between 25 and 29.9, of “normal” weight in the range of 18.5 to 24.9, or underweight if lower than 18.5.
While BMI is easy to calculate, one of its main limitations is that it cannot distinguish between muscle and fat mass, the researchers noted.
“People who are bodybuilders can really elevate their body mass index,” one doctor said. “But they’re healthy even with a BMI indicating that they’re obese.” (iStock)
“For example, people who are bodybuilders can really elevate their body mass index,” Orlando said. “But they’re healthy even with a BMI indicating that they’re obese.”
“BMI is just so ingrained in how we think about body fat,” Mainous added. “I think the study shows it’s time to go to an alternative that is now proven to be far better at the job.”
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Other methods, such as a DEXA (dual-energy X-ray absorptiometry) scan, may be even more accurate than BIA, but are much more expensive and not as accessible, the researchers noted.
“If you talk to obesity researchers, they’re going to say you have to use the DEXA scan because it’s the most accurate,” Mainous said in the release. “And that’s probably true. But it’s never going to be viable in a doctor’s office or family practice.”
“It has been an easy measurement tool that helps us understand at-risk groups across various populations and demographics, but it doesn’t provide accurate data from patient to patient,” a doctor said of BMI. (iStock)
Dr. Stephen Vogel — a family medicine physician with PlushCare, a virtual health platform with primary care, therapy and weight management options — echoed the limitations of BMI.
“It has been an easy measurement tool that helps us understand at-risk groups across various populations and demographics, but it doesn’t provide accurate data from patient to patient,” the North Carolina-based doctor, who was not involved in the study, told Fox News Digital.
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“These findings don’t challenge the assumptions about BMI — they strengthen the message that new standards, delivered in a consistent and low-cost way, would provide better nuance for the individual when it comes to their overall physical health.”
Potential limitations
“The main strengths of this study are a better correlation to an individual’s risk of morbidity and mortality — however, the limitations lie in the fact that we don’t have enough data to determine the right cutoff for these numbers, or to identify the right tools that will be both accurate and precise across the population,” Vogel said.
The researchers also acknowledged that body fat percentage thresholds haven’t yet been as standardized as BMI and waist circumference.
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Also, the age range of the participants in the study was limited by the data source.
“Future studies should extend this comparison of body fat to BMI in older adults,” the researchers wrote.
“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,” a doctor said. (iStock)
The study was also limited by focusing only on mortality as an outcome, they noted, without taking into account any developing diseases — such as heart failure or cancer — that could deepen the understanding of body fat as a risk factor.
The goal, according to Vogel, is to have a cost-effective, consistent method that can be used across the population with reliable accuracy.
“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.”
“Benefits would come in the form of a more detailed list of information that helps providers and patients make informed decisions about the patient’s health, which is ideal,” Vogel noted.
“I’m hopeful there’s enough buzz around these measures that steps will continue to be taken toward regular implementation.”
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The researchers are hopeful that once standards are validated, measuring body fat percentage with bioelectrical impedance analysis could become standard of care.
They added, “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.”