Measuring levels of a chemical found in blood offers the best indicator yet of the amount of fat surrounding abdominal organs, according to a new study of lean and obese individuals reported in the July issue of Cell Metabolism, a publication of Cell Press. The buildup of such visceral fat is of particular health concern as it has been linked to insulin resistance, type 2 diabetes, and heart disease risk.
The researchers, including Barbara Kahn and Timothy Graham of Harvard Medical School and Matthias Blher of the University of Leipzig in Germany, showed that retinol-binding protein 4 (RBP4) is produced in much greater amounts by visceral fat compared to the subcutaneous fat that lies just beneath the skin. Moreover, they report that blood serum levels of RBP4 jump in people who are obese, who have double or even triple the concentrations found in individuals of normal weight.
We believe that in the near future, measurements of RBP4 serum concentrations might serve as a novel biomarker for visceral obesity and increased risk for type 2 diabetes and other adverse outcomes of visceral obesity, said Blher. In addition, pharmacological interventions that reduce RBP4 levels might be a new approach in the treatment of metabolic syndrome and visceral obesity.
Prior to 2005, when Kahns group showed that elevating RBP4 levels in mice causes insulin resistance and lowering them in obese mice can improve insulin sensitivity, the only known function of RBP4 was to carry vitamin A (also known as retinol) in the blood, Kahn said.
The researchers went on to show that serum RBP4 concentrations are also elevated in insulin-resistant individuals with obesity, type 2 diabetes, or impaired glucose tolerance, and even in otherwise normal people with a strong family history of diabetes. Likewise, interventions designed to improve insulin sensitivity, such as exercise training, lifestyle modification, or gastric banding surgery also lead to a d
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