BOSTON — In the ongoing debate over the best way to measure health risks associated with weight, the body mass index (BMI) has long been a staple. Health professionals have traditionally used BMI as a quick screening tool to identify patients at risk of future health problems due to their weight. However, a new study suggests that BMI may not be the most accurate measure, and a different approach could offer a better prediction of health risks.
The issue with BMI lies in its method of calculation, which uses only height and weight. This can lead to misleading results, as muscle and bone weigh more than fat. Consequently, BMI can overestimate health risks for individuals with a muscular build or larger frame, while underestimating risks for older adults or those who have lost muscle mass. According to the Harvard T.H. Chan School of Public Health in Boston, these limitations highlight the need for more precise measurement tools.
Introducing Bioelectrical Impedance Analysis
Researchers are now advocating for bioelectrical impedance analysis (BIA) as a more accurate method of assessing health risks. BIA measures not just body fat percentage but also lean muscle mass and water weight using undetectable electric currents. This technology involves standing on metal plates while holding a metal attachment, allowing the machine to send a weak electrical current through the body. Different tissues conduct electricity differently, enabling the machine to calculate body composition.
“We found body-fat percentage to be a stronger predictor of 15-year mortality risk in adults between the ages of 20 and 49 than BMI,” said Arch Mainous III, lead author of the study published in the journal Annals of Family Medicine. The study revealed that individuals with high body fat as measured by BIA were
262% more likely to die from heart disease
than those with a healthy body fat percentage.
The Limitations of BMI
BMI is calculated by dividing a person’s weight by the square of their height. While it is effective on a population level, correlating with chronic diseases such as cancer, heart disease, and diabetes, it falls short at the individual level. For instance, someone who appears thin but has a high internal fat content, often referred to as “skinny fat,” may have a normal BMI despite being at risk for health issues.
“Those people are more likely to have nonalcoholic fatty liver disease, elevated glucose, and blood pressure,” Mainous explained. These conditions can be managed or even reversed if detected early. Despite these drawbacks, BMI remains popular among doctors due to its low cost and ease of use, compared to more expensive and less accessible methods like DEXA scans.
Potential for Change in Medical Practice
While DEXA scans are considered the gold standard for body mass analysis, their high cost and limited availability make them impractical for widespread use. In contrast, newer versions of bioelectrical impedance machines are proving to be both accurate and cost-effective. “We found the newer versions of bioelectrical impedance are pretty accurate, giving some valid and reliable results,” said Dr. Frank Orlando, senior author of the study.
However, Dr. Andrew Freeman, director of cardiovascular prevention and wellness at National Jewish Health in Denver, cautions against relying on at-home BIA devices, which can be affected by factors like hydration levels. “At-home measurements will only give a ballpark — the clinic-based machines are more precise,” Freeman noted.
Implications for Future Health Assessments
The study analyzed data from 4,252 participants of the National Health and Nutrition Examination Survey (NHANES) conducted between 1999 and 2004. Researchers compared this data with the National Death Index through 2019, adjusting for variables like age, race, and poverty status. They found that a BMI indicating obesity was not associated with a statistically significant higher risk of death, while high body fat measured by BIA was linked to a
78% higher risk of death from any cause
.
These findings suggest a potential shift in how medical professionals assess health risks related to body composition. “It’s a no-brainer for doctors to use bioelectrical impedance analysis on patients,” Orlando concluded. As the medical community continues to explore more accurate methods of health assessment, BIA may become a standard tool in evaluating patient health risks.
