Introduction to Body Fat and Health Risks
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.
Limitations of BMI
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. 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.
Comparison of Body Fat and BMI
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. 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.
Understanding Body Fat Measurement
A new study from the University of Florida found that instead of using body mass index (BMI), one’s level of body fat is “far more accurate” when examining death risk. BMI, used to determine whether a person’s weight is in a healthy range for their height, was described as “entirely unreliable” in predicting the risk of death over a 15-year period.
Limitations of BMI in Measuring Health
“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. “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.
Alternative Methods for Measuring Body Fat
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. “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.”
Expert Insights on Body Fat and Health
“People who are bodybuilders can really elevate their body mass index,” senior author Frank Orlando, M.D., said about the limitations of BMI. “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,” Arch Mainous, PhD, Professor and Vice Chair of Research in the Department of Community Health and Family Medicine at the University of Florida, 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.”
Potential Limitations of the Study
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.” 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.
Future Directions for Body Fat Measurement
“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. Also, the age range of the participants in the study was limited by the data source.
Conclusion
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. According to Dr. Stephen Vogel, “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.” “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.”
FAQs
- Q: What is the main limitation of using BMI to measure health risks?
A: The main limitation of using BMI is that it cannot distinguish between muscle and fat mass. - Q: What method did the researchers use to measure body fat in the study?
A: The researchers used bioelectrical impedance analysis (BIA) to measure body fat. - Q: What is the potential benefit of using body fat percentage instead of BMI?
A: Using body fat percentage could provide a more accurate measurement of health risks and help providers and patients make informed decisions about health. - Q: What is the goal for future studies on body fat measurement?
A: The goal is to have a cost-effective, consistent method that can be used across the population with reliable accuracy.
