Lecithin

Lecithin is any of a group of yellow-brownish fatty substances occurring in animal and plant tissues, and in egg yolk, composed of phosphoric acid, choline, fatty acids, glycerol, glycolipids, triglycerides, and phospholipids.

Lecithin is an integral part of cell membranes, and can be totally metabolized, so it is virtually non-toxic to humans. There are studies that show soy-derived lecithin has significant effects on lowering cholesterol and triglyceride, while increasing HDL ("good cholesterol") levels in the blood.