Israeli researchers are challenging the prevailing use of the Body Mass Index as a measure of obesity, suggesting that body fat percentage is a more accurate indicator of an individual’s overall health. The findings further suggest that one-third of people currently considered of normal weight are actually obese.
The study comes at a pivotal time. A report released by the World Obesity Atlas in March predicted that more than 4 billion people—51% of the world’s population—will be obese by 2035. The report also estimated that the cost of treating obesity-related medical conditions will climb to $4 trillion per year.
And in June, the American Medical Association called BMI “an imperfect way to measure body fat in multiple groups given that it does not account for differences across race/ethnic groups, sexes, genders and age-span.”
The Tel Aviv University study, led by professor Yiftach Gepner and PhD student Yair Lahav, in collaboration with Aviv Kfir, examined data from approximately 3,000 Israeli women and men, making it the largest study of its kind conducted in Israel. The findings, published in the peer-reviewed “Frontiers in Nutrition,” call for redefining the standard for assessing obesity, and equipping clinics with devices to measure body fat percentage.
For years, the BMI has been widely used in clinics as a standard measure of an individual’s general health. The Center for Disease Control explains that BMI is calculated by “a person’s weight in kilograms (or pounds) divided by the square of height in meters (or feet).”
In contrast, calculating body fat percentage is more complicated and can involve a combination of various measurements and tests.
These might include body circumference measurements, dual-energy x-ray absorptiometry, skinfold calipers to measure fat by pinching the skin, hydrostatic weighing to measure a body’s density and bioelectrical impedance analysis, which involves placing electrodes on a person’s skin.
The researchers discovered a significant disparity between BMI and body fat percentage, leading to what they call “the paradox of obesity with normal weight.” This phenomenon refers to individuals who have excess body fat despite falling within the normal weight range according to the BMI.
The study found that of the participants classified as having a normal weight, 38.5% of women and 26.5% of men were identified as “obese with normal weight” based on their body fat percentage. These individuals had high levels of sugar, fat and cholesterol in their blood, indicating an increased risk for cardiometabolic diseases such as heart disease, diabetes, fatty liver and kidney dysfunction.
Surprisingly, the research also revealed that 30% of men and 10% of women classified as overweight had a normal body fat percentage.
“Our findings were somewhat alarming, indicating that obesity with normal weight is much more common in Israel than we had assumed,” said Gepner.
“Moreover, these individuals, who are within the normal range according to the prevailing BMI index, usually go unnoticed. They do not receive the necessary treatment or guidance to change their nutrition or lifestyle, putting them at an even greater risk for cardiometabolic diseases,” he said.
Based on the results, the researchers argue that body fat percentage should replace BMI as the standard measure of obesity and overall health.
They also recommend the use of convenient and accessible tools such as skinfold measurements, which estimate body fat based on the thickness of the fat layer beneath the skin, and user-friendly devices that measure the body’s electrical conductivity, already in use at many fitness centers.
“Our study found that obesity with normal weight is very common in Israel, much more than we had previously assumed, and is significantly correlated with substantial health risks,” explained Gepner.
“We also found that body fat percentage is a much more reliable indicator than BMI for assessing an individual’s general health. Therefore, we recommend equipping all clinics with suitable devices for measuring body fat content and gradually establishing it as the gold standard in Israel and worldwide to prevent disease and premature mortality.”