Apolipoprotein C-1 directly interferes with fatty acid uptake and is a major plasma inhibitor of cholesterol ester transfer protein. Apolipoprotein C-I has been used to develop a quantitative strategy, named secretome-derived isotopic tag (SDIT), to concurrently identify and quantify the adipocyte-secreted plasma proteins from normal and high-fat-diet (HFD) induced obese mice.