Researchers have found that measuring levels of retinol-binding protein 4 (RBP4), found in blood, is a good indicator of the amount of fat surrounding abdominal organs. The buildup of such visceral fat has been linked to insulin resistance, type 2 diabetes, and heart disease risk.
The team from Harvard Medical School and the University of Leipzig observed that RBP4 in the blood rose along with its gene expression activity in fat and intra-abdominal fat mass, independent of age, gender, and body mass index. Among several fat-secreted proteins considered to be important in regulating insulin/glucose balance, serum RBP4 concentrations appear to be the best indicator of insulin resistance and intra-abdominal fat mass, the researchers concluded.
The scientists examined 196 people and noticed that RBP4 is preferentially produced in deep fat that covers organs of the belly. RBP4 gene expression activity levels spiked about 60-fold in the visceral fat of viscerally obese volunteers relative to lean study participants. Also, visceral fat RBP4 concentrations were increased 12-fold in obese individuals with a preponderance of subcutaneous fat.
The study is published in the July issue of Cell Metabolism.