Researchers at Tel Aviv University (TAU) have found that the widely used Body Mass Index (BMI) measurement – a person’s weight in kilograms divided by the square of height in meters – is less sensitive for determining obesity than what doctors previously thought.The researchers urge that community health and hospital outpatient clinics be equipped with devices for measuring body-fat percentage, and call for ultimately turning this index into the gold standard of obesity measurements (in Israel and worldwide).Researchers from the School of Public Health at TAU’s Faculty of Medicine examined the anthropometric data of about 3,000 Israeli women and men and concluded that body-fat percentage is a much more reliable indicator of an individual’s overall health and cardiometabolic risk than the BMI index.The study – the largest of its kind ever conducted in Israel – was led by Prof. Yftach Gepner and doctoral student Yair Lahav, in collaboration with Aviv Kfir. It was based on data from Tel Aviv’s Yair Lahav Nutrition Center and published in Frontiers in Nutrition under the title “The paradox of obesity with normal weight; a cross-sectional study.”
“Israel is a leader in childhood obesity and more than 60% of the country’s adults are defined as overweight,” said Gepner. “The prevailing index in this respect is BMI, which is considered a standard indicator of a person’s general health. But despite the obvious intuitive connection between excess weight and obesity, the actual measure for obesity is the body’s fat content, with the maximum normal values set at 25% for males and 35% for females.”
How is obesity defined?
Higher fat content in a person is defined as obesity, and can cause a range of potentially life-threatening cardiometabolic diseases including heart disease, type-2 diabetes, fatty liver, kidney dysfunction, and more. The disparity between the two indexes has generated a phenomenon called “the paradox of obesity with normal weight” – higher than normal body fat percentage in normal-weight individuals. In this study, the team examined the prevalence of this phenomenon in Israel’s adult population.A number of elements may influence the large variation of body fat mass for the same body weight, they wrote. “The main known factors are genome-related issues; the loss of skeletal muscle mass with aging; ethnicity-related body shape and composition; the level of exercise training, where fat-free mass is increased by resistance training and decreased by aerobic exercise; and somatotype, which provides a quantitative description of body shape independently of body size and can be classified as fat (endomorphy), muscular (mesomorphy), or linear (ectomorphy).They analyzed the anthropometric data (the scientific study of the measurements and proportions of the human body) of 3,000 Israeli women and men that had been collected over several years – BMI scores; DXA scans (X-rays used to measure body composition, including fat content); and cardiometabolic blood markers.About one third of the participants were found to be within the normal weight range. Of these, 38.5% of the women and 26.5% of the men were identified as “obese with normal weight” – having excess fat content despite their normal weight. Matching body fat percentage with blood markers for each of these individuals, the study found a significant correlation between ‘obesity with normal weight’ and high levels of sugar, fat, and cholesterol – major risk factors for a range of cardiometabolic diseases. At the same time, 30% of the men and 10% of the women identified as overweight were found to have 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,” Gepner declared. “Moreover, these individuals, being within the norm according to the prevailing BMI index, usually pass ‘under the radar,’ Unlike people who are identified as overweight, they receive no treatment or instructions for changing their nutrition or lifestyle – which places them at an even greater risk for cardiometabolic diseases.”Based on their findings, the researchers concluded that body fat percentage is a more reliable indicator of a person’s general health than BMI. Consequently, they suggest that body fat percentage should become the prevailing standard of health, and recommend some convenient and accessible tools for this purpose: skinfold measurements that estimate body fat based on the thickness of the fat layer under the skin; and a user-friendly device measuring the body’s electrical conductivity that is already used in many fitness centers.