A new study has found that body fat percentage is a far more accurate indicator of health risks than the widely used body mass index (BMI).
“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.
The research suggested that relying solely on BMI — a simple height-to-weight ratio — may overlook critical health dangers, particularly for those with hidden fat.
Researchers analysed data from 4,252 US adults who took part in the National Health and Nutrition Examination Survey (NHANES) between 1999 and 2004 (1999-2004) and tracked mortality through 2019.
They compared three body composition measures — BMI, body fat percentage, and waist circumference — to determine which one best indicated long-term health risks.
The researchers then matched the health data with records from the National Death Index through 2019 to see how many participants had died.
After adjusting for factors like age, race, and poverty level, the study found that people classified as obese by BMI did not have a significantly higher risk of death compared to those in the healthy BMI range.
However, individuals with high body fat measured using a more precise method called bioelectrical impedance analysis were found to be 78% more likely to die from any cause and 262% more likely to die from heart disease.
The study further suggested that bioelectrical impedance analysis (BIA) is a stronger predictor of mortality than the widely used BMI.
BIA uses undetectable electric currents to measure not only the percentage of body fat but also lean muscle mass and water weight.
The BIA machine also uses algorithms to estimate body fat, muscle mass, and water weight by measuring how a weak electrical current passes through different tissues in the body.
The study explained that the problem with BMI lies in its inability to detect hidden health risks, especially in individuals who appear thin but have harmful fat around their internal organs.
“Those people are more likely to have nonalcoholic fatty liver disease, more likely to have elevated glucose, more likely to have elevated blood pressure, and more likely to have inflammation in general,” Arch Mainous III, lead author of the study, said.
Mainous argued that while most doctors are aware of BMI’s limitations, many continue to rely on it “because it is cheap and easily put into practice”.
He said there is the option of a more direct measurement called the DEXA scan, but its high cost makes it impractical for routine use.
However, Andrew Freeman, director of cardiovascular prevention and wellness at National Jewish Health in Denver, cautioned against relying on at-home bioelectrical impedance devices, saying they are “not as accurate as clinical ones”.
“They can be affected a lot by how much body fluid you have, how hydrated you are. At-home measurements will only give a ballpark, the clinic-based machines are more precise,” he said.
BIA is recommended because it can help identify health risks more accurately, leading to better prevention and early intervention for serious health conditions.
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