High-density lipoprotein (
HDL) is one of the five major groups of
lipoproteins. Lipoproteins are complex particles composed of multiple proteins which transport all
fat molecules (
lipids) around the body within the water outside cells. They are typically composed of 80-100 proteins/particle (organized by one, two or three
ApoA; more as the particles enlarge picking up and carrying more fat molecules) and transporting up to hundreds of fat molecules/particle. Unlike the larger lipoprotein particles which deliver fat molecules to cells, HDL particles remove fat molecules from cells which want to export fat molecules. The fats carried include
cholesterol,
phospholipids, and
triglycerides; amounts of each quite variable.