Lecithin is a natural substance found in cell membranes and is manufactured in the liver from dietary choline. It contains a mixture of phosphatides, including phosphatidyl choline, an important precursor to the main neurotransmitter, acetylcholine. In addition, the body utilizes lecithin both for the proper formation of bile (the body's main emulsifying compound), and as an emulsifying agent itself. As an emulsifier, lecithin helps in the absorption and utilization of fat-soluble nutrients, such as vitamins A, D, E and K.