One of the key indicators of ill health remains one of the most sensitive topics to talk about openly—our weight. For years, health professionals have relied on the body mass index (BMI) to assess weight and its link to health risks, but this approach is now set to evolve.

Earlier this year, we published an article exploring the definition and diagnosis of obesity, highlighting the limitations of using BMI as a standalone measure. The authors explained that simply having a larger body should not automatically result in a diagnosis of “clinical obesity.”

Now, just six months later, the entire conversation around body weight measurement has shifted once again. If the findings of a new study gain widespread acceptance, BMI may soon become obsolete, giving way to the adoption of BIA.

BIA, or bioelectrical impedance analysis, measures the resistance (or impedance) of body tissues using a small, harmless electrical current. It can gather the following information:

• Body fat percentage
• Muscle mass
• Water content
• Bone mass

There are several benefits to be had here. These include a more accurate reflection of body composition (fat vs. lean mass) and, according to the latest study, a much more precise insight into health risks.

During the measurement process, the patient stands on metal plates attached to the machine and holds metal sensors—often with their hands or thumbs—positioned away from the body. Once the test begins, the machine passes a low-level electrical current through the body. Because body fat, muscle, and bone each conduct electricity differently, the machine analyses the data using algorithms to calculate lean muscle mass, body fat percentage, and water content.

“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 Tuesday in the journal Annals of Family Medicine.

When it came to deaths from heart disease, people with high body fat as measured by BIA were 262 per cent times more likely to die than people who had a healthy percentage of body fat, said Mainous, a professor and vice chair of research in community health and family medicine at the University of Florida School of Medicine.

Paving the way

The study findings pave the way for much earlier intervention in groups that were not (at least on the BMI scale) necessarily considered to be at risk.

Using BMI to assess health risks is effective when applied at the population level. Numerous studies have demonstrated that a higher BMI is genuinely associated with an increased risk of developing various chronic diseases, including cancer, heart disease, type 2 diabetes, kidney disease, liver disease, and others.

However, BMI falls short in evaluating individual patients. For example, someone might appear thin outwardly but have significant internal fat surrounding vital organs—a condition sometimes called “skinny fat.” In such cases, their BMI may suggest they’re healthy, while they could actually be at serious risk.

BMI is measured by dividing your weight by the square of your height. (For the mathematically challenged, the National Institutes of Health has a free calculator.)

The new study analysed data on 4,252 men and women who participated in the 1999 to 2004 federal survey called NHANES, or the National Health and Nutrition Examination Survey, a yearly checkup of the nation’s health.

Technicians measured each person’s body composition, including height, weight and waist circumference. In addition, all participants underwent a clinic-based bioelectrical impedance analysis.

Researchers then compared that data with the National Death Index through 2019 to determine the number of deaths. After adjusting for age, race and poverty status, the study found that a BMI labelled as obese was not associated with a statistically significantly higher risk of death from any cause, when compared with those in the healthy BMI range.

People with high body fat as measured by bioimpedance analysis, however, were 78 per cent more likely to die from any cause, Mainous said. Measuring waist circumference was also helpful, but not as accurate as body mass.

Add to that the 262 per cent higher chance of dying from heart disease found by the study, and it seems like a no-brainer for doctors to use bioelectrical impedance analysis on patients.