BOSTON — BMI, or body mass index, often draws criticism from health experts. Despite its flaws, it has been widely utilized as a screening tool for flagging patients at risk of serious health issues due to their weight.
The problem is that BMI determines risk solely based on height and weight. This method can misrepresent the health of those with muscular builds or larger frames, potentially exaggerating their risks. On the flip side, it tends to underestimate risks for older adults and those who have lost muscle mass, according to researchers from the Harvard T.H. Chan School of Public Health.
A new study suggests a more reliable measurement approach might be bioelectrical impedance analysis (BIA). This method uses low-level electric currents to assess body fat percentage, lean muscle mass, and water weight.
The process involves standing on metal plates while gripping attachments that send a weak electrical current through the body. Since fat, muscle, and bone conduct electricity differently, the machine can calculate various body composition metrics using its algorithms.
Arch Mainous III, the lead author, noted, “We found body-fat percentage better predicts mortality risk over 15 years for adults aged 20 to 49 than BMI.” The study, published in the journal Annals of Family Medicine, indicates that those with high body fat were 262% more likely to die from heart disease compared to those with healthy body fat percentages.
“Using BMI didn’t indicate any risk in this younger demographic, who, I mean, we generally don’t think of as high-risk for heart issues,” senior author Dr. Frank Orlando remarked, highlighting the potential for early health interventions. “I think it’s a game changer for how we should consider body composition,” he added.
The problem with BMI
BMI is calculated by dividing weight in kilograms by height in meters squared. For those not mathematically inclined, the National Institutes of Health provides a handy calculator.
In BMI terms, a score between 18.5 and 24.9 indicates a healthy weight, while 25 to 29.9 denotes overweight; 30 to 34.9 is classified as obesity, 35 to 39.9 as class 2 obesity, and anything above 40 as severe or class 3 obesity. Individuals with a BMI below 18.5 are considered underweight.
While BMI can provide useful insights on a population level, it often falls short on an individual basis. Consider someone who appears fit but has hidden fat surrounding their organs—this person’s BMI might look fine, yet their health could be at serious risk.
According to Mainous, such individuals are prone to several health issues, including nonalcoholic fatty liver disease and elevated blood pressure, all of which can potentially be treated or even reversed with early detection.
Many doctors, while aware of BMI’s limitations, still opt for it since it’s cost-effective and easy to implement. “They would prefer a more accurate method like a DEXA scan, but those are expensive and not always accessible,” Mainous noted.
DEXA, or dual-energy X-ray absorptiometry, is regarded as the gold standard for body composition analysis, with machine costs ranging from $45,000 to $80,000. As a result, patients often have to visit hospitals for scans that can run between $400 and $500.
“However, newer bioelectrical impedance devices can yield fairly accurate results,” Orlando mentioned, although he cautioned that home-based products lack precision.
Dr. Andrew Freeman, who was not involved in the study, pointed out that at-home measurements could vary based on hydration levels and other factors, making them less reliable than clinic-based assessments.
Is it time for doctors to embrace body fat measurements?
This study looked at data from 4,252 participants spanning the 1999 to 2004 NHANES, which is a comprehensive national health check-up.
Participants’ body compositions were evaluated, including height, weight, and waist size, alongside clinic-based bioelectrical impedance analysis. Researchers then matched this data with the National Death Index through 2019 to see mortality outcomes. After accounting for age, race, and socioeconomic status, the analysis indicated that a BMI classification of obesity did not correspond with a significantly higher mortality risk when set against those in a healthy weight range.
In contrast, those with high body fat measured via bioimpedance analysis were found to be 78% more likely to die from any cause. While waist circumference offered additional insights, it wasn’t as definitive as body fat measurements.
When combined with the alarming 262% elevated risk of heart disease-related deaths indicated by the study, it seems prudent for doctors to adopt bioelectrical impedance analysis in patient evaluations, according to Orlando.
