The molecules we eat. (a) Lecithin is essential in common foods, such as chocolate. (b) Lecithin consists of lipid molecules, such 1-palmitoyl-2-oleoylphosphatidylcholine and 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine. (c) Lipid molecules spontaneously assemble into lipid bilayers, as shown in this schematic illustration. Lipid bilayers are the foundation of biological membranes that delineate cells and intracellular organelles.