A new study from Tel Aviv University (TAU) and the Dana Dwek Children’s Hospital in Tel Aviv has shown that disease can be prevented in children with obesity by maintaining a low percentage of fat in the liver.

The researchers used innovative methods to examine 31 Israeli children with obesity in an attempt to understand why some have developed illnesses as a result of their excess weight while others have remained healthy. They discovered that the percentage of fat in the livers of children already experiencing illness was two and a half times higher — 14% compared to 6% — vs. the group of healthy obese children.

The groundbreaking study was led by Professor Yftach Gepner and doctoral student Ron Sternfeld of TAU’s Gray Faculty of Medical & Health Sciences and its Sylvan Adams Sports Science Institute, together with Professor Hadar Moran-Lev and Professor Ronit Lubetzky of the Dana Dwek Children’s Hospital. The findings were published on July 8, 2025, in the journal Frontiers in Nutrition.

The researchers say that, according to the findings, the health of obese children is influenced not only by the quantity but also by the quality and composition of the food they eat. It indicates that even if obese children do not lose weight or reduce their food intake, their health can be protected by monitoring the components of their diet and minimizing fatty liver damage.

“This is a cross-sectional study, which means we did not follow the children over time but rather examined them thoroughly at one point in time,” Sternfeld says. “Therefore, we can only indicate correlation but not causality in our findings. Nonetheless, the study is important and unique, investigating why some obese children remain metabolically healthy, while others of the same weight already show signs of metabolic disease.”

The researchers conducted a wide range of medical tests and reviewed the children’s medical records dating back to the prenatal stage. The highlight of the study was the use of MRS technology, an advanced non-invasive method that directly assesses liver composition and enables precise measurement of liver fat percentage during MRI scans. This is one of the few studies ever to use MRS for diagnosing fatty liver in obese children.

To identify the best predictor of metabolic disease in obese children, the researchers examined 31 children treated at the Obesity Clinic of Dana Dwek’s Gastroenterology Institute. The children were similar in age and body weight, but one group was still metabolically healthy while the other already showed abnormal rates of fasting glucose, blood lipids, cholesterol, and/or blood pressure. The researchers found that the factor most associated with metabolic illness was the percentage of fat in the liver: 14% in children already showing illness, compared to only 6% in the group of obese but still healthy children.

“We checked many different criteria and found no difference between the two groups,” Sternfeld continues. “For example, we found no difference in the visceral fat which surrounds internal organs in the abdomen, considered a major metabolic risk indicator. In contrast, a dramatic gap was found in the percentage of fat in the liver.

“Fatty liver is defined as a condition where more than 5.5% of the liver is composed of fat. Linked to diabetes, high blood pressure, sleep apnea, and more, fatty liver is considered one of the main causes of illness associated with obesity. To our surprise, we found that some obese children do not have fatty liver.”

While this finding is difficult to explain, some hypotheses can be suggested. “Comparing the children’s diets, we found that those already ill consume higher levels of sodium, processed food, and certain saturated fatty acids from animal protein, mainly red meat,” Professor Gepner says. “This means that the quality, not just the quantity, of the food plays a role. A Mediterranean diet may provide protection against metabolic illness, even in the case of obesity.

“Another possibility has to do with the children’s medical history: we found that three times as many children in the ‘unhealthy obesity’ group, compared to those still healthy, had been born following high-risk pregnancies. Whatever the precise cause, our study strengthens the hypothesis that the liver is the most important metabolic organ and should be a primary target for preventive medicine.”