Lipids, also known as fats, are small molecules derived from biochemical subunits from either the ketoacyl or isoprene groups. Creating eight distinct categories: fatty acids, glycerolipids, glycerophospholipids, sphingolipids, saccharolipids, and polyketides (derived from condensation of ketoacyl subunits); and sterol lipids and prenol lipids (derived from condensation of isoprene subunits). Their primary purpose is to store energy over the long term. Due to their unique structure, lipids provide more than twice the amount of energy that carbohydrates do. Lipids can also be used as insulation. Moreover, lipids can be used in hormone production to maintain a healthy hormonal balance and provide structure to cell membranes.