Lipid

Lipids are a class of natural, organic compounds in plants and animals, defined by a specific way they behave: they are soluble in non-polar solvents. That is, lipids are not soluble in water but dissolve in solvents like gasoline, ether, carbon tetrachloride, or oil. The vast majority of lipids are colorless and mostly fats and oils.

Lipids comprise one of the three broad classifications into which nourishing substances can be broken. Lipids, proteins, and carbohydrates are the three very general classifications. Fiber may be filling but is not called nourishment. Lipids are rich in energy, supplying twice the caloric value per unit weight than carbohydrates or proteins. Seeds contain lipids as energy storage substances to get the plant started.

Lipids are derived from living systems of plants, animals, or humans. Substances that are lipids may also be called fat-soluble. For example, this designation is frequently applied to those vitamins in our food that a human can store in body fat. This is contrasted with the vitamins that are not lipid-like, but are instead water soluble. Excesses of the water soluble vitamins are passed in one's urine and must be replaced frequently. The fat-soluble, lipid-like vitamins do not need to be taken daily. (The common known fat-soluble vitamins are vitamins A, D, E, and K.)