Many different types of molecules in the body, such as fats, waxes, and fat-soluble vitamins, fall into the category of lipids.. Energy storage is the most common of the many functions of lipids, though they can also provide cellular structure or act as signaling molecules.Other important but less common functions of lipids in the body include enzyme activation, molecular transportation, and metabolism.Humans must consume lipids as a part of their diets because of the nutrients they contain and because some fats are required in order to store fat-soluble vitamins.nergy storage and cell membrane formation are the two most prominent functions of lipids in the body, but there are other functions.