Tel Aviv University study argues third of normal-weight Israelis are secretly obese

Researchers urge doctors to use overall body fat composition, rather than body mass index, to more accurately determine patients’ health risks

Renee Ghert-Zand is the health reporter and a feature writer for The Times of Israel.

Illustrative: Feet on a scale (Tero Vesalainen; iStock by Getty Images)
Illustrative: Feet on a scale (Tero Vesalainen; iStock by Getty Images)

Looks can be deceiving, according to a new study by the School of Public Health at Tel Aviv University’s Faculty of Medicine. Though one may appear from the outside to be of normal weight, it argues, they may actually be effectively obese on the inside.

The research led by Prof. Yftach Gepner indicates that one-third of Israelis of normal weight according to the prevailing BMI (body mass index) measurement method are actually obese when overall body fat composition is taken into consideration. He published his findings in the peer-reviewed Frontiers in Nutrition journal.

It is estimated that 64 percent of Israelis are overweight or obese, according to World Health Organization standards. The WHO determines these categories based on the easy-to-measure BMI method, which is calculated by dividing a person’s weight in kilograms by the square of their height in meters.

“We are dealing with an obesity epidemic…But we might be misclassifying the prevalence of obesity… We should be using more accurate assessments, which give us direct information on the amount of adipose tissue a person has,” Gepner said.

According to Gepner, it’s the fat within our bodies — how much we have, where it is, and what it is doing — that has a critical bearing on our health.

The normal maximum values for body fat content are set at 25% for males and 35% for females. Higher fat content is defined as obesity and can cause a range of potentially life-threatening cardio-metabolic diseases: heart disease, diabetes, fatty liver, kidney dysfunction and more.

Gepner, PhD student Yair Lahav and colleague Aviv Kfir analyzed the accumulated anthropometric data of 3,001 Israeli men and (non-pregnant) women ages 20-95 recruited for the study over several years.

The data included BMI scores, DXA scans (using X-rays to measure body composition, including fat content), abdominal circumference measurement, and cardiometabolic blood markers. The latter included blood tests for glycemic control, lipids, liver enzymes, and blood count.

About one-third of the participants, 1,000 individuals, 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. These normal-weight individuals had high levels of sugar, fat, and cholesterol, which put them at risk for disease.

At the same time, 30% of the men and 10% of the women identified as overweight were found to have a body fat percentage within the normal range.

Prof. Yftach Gepner (Courtesy of Tel Aviv University)

Worried that many normal-weight individuals are “flying under the radar” and not receiving medical advice to make lifestyle changes to reduce their fat composition, Gepner recommends that physicians change their approach.

“By shifting in the clinic from BMI assessment to body composition assessment, we’ll pick up diagnostic abnormalities even before we can see those changes in the blood,” he said.

Such a shift would not necessitate a huge investment. He recommends that doctors equip their offices with skinfold calipers, which are an inexpensive and fairly accurate tool for measuring body fat composition.

“There are also bioelectrical impedance analysis devices that measure the resistance of electrical waves in the body. Fat offers more resistance to these waves than say water. A lot of fitness centers have these already,” Gepner said.

“If a clinic makes the decision that it’s time in 2023 to move forward to the next level of accuracy in assessing their patients, they should have easy, fast, and relatively cheap devices to measure body composition,” he said.

Gepner said these devices range in price from $250 to $5,000, with the higher-priced ones being more accurate.

Prof. Robert Klempner, director of the Israeli Center for Cardiovascular Research and director of the Cardiac Rehabilitation Institute at Sheba Medical Centre, noted that the value of the TAU study is limited by the fact that it is not connected to clinical outcomes.

Illustrative photo of the Tel Aviv University campus. (Andrew Tobin/JTA)

“As a cardiologist, I would ask whether we have enough evidence indicating that this is strongly and independently associated with heart clinical endpoints or events,” said Klempfner, who reviewed the study at The Times of Israel’s request.

“Does this actually and independently of other features increase heart outcomes like myocardial infarction [heart attack], stroke, urgent catheterizations, and the like? Because just another risk factor… if it’s not independent and not really associated with outcomes, it’s a little less interesting,” he said.

While Klempfner expressed his doubts about the study’s implications for heart health, Gepner focused on the liver. “Losing 3% of body weight with exercise and a healthy diet can contribute to a 30% loss of the fat in the liver, which is the key organ controlling metabolism,” he said.

The results of Gepner’s study don’t mean we should get rid of our bathroom scale just yet, but perhaps the number we see there doesn’t tell us all we need to know.

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