Fat, any substance of plant or animal origin that is nonvolatile, insoluble in water, and oily or greasy to the touch. Fats are usually solid at ordinary temperatures, such as 25 °C (77 °F), but they begin to liquefy at somewhat higher temperatures. Chemically, fats are identical to animal and vegetable oils, consisting primarily of glycerides, which are esters formed by the reaction of three molecules of fatty acids with one molecule of glycerol .Palmitic acid is one of the most prevalent fatty acids occurring in the oils and fats of animals; it also occurs naturally in palm oil. It is generated through the addition of an acetyl group to multiple malonyl groups connected by single bonds between carbons. This structure forms a saturated acid-a major component of solid glycerides. Together with oils, fats comprise one of the three principal classes of foodstuffs, the others being proteins and carbohydrates. Nearly all cells contain these basic substances. Fat is sometimes called nature's storehouse of energy because on a weight basis it contains more than twice as much energy as does carbohydrate or protein. It is probably as storehouses or depots of concentrated energy that fats appear in plant reproductive organs, such as pollen grains and seeds. It is this fat that humans recover from plants for use as food or in industry. The fat content of the non-reproductive tissue of plants is usually so low that recovery is impracticable. Yet much dietary fat comes from natural foodstuffs without being separated from the other plant materials with which it occurs. The proportion of fat in these foodstuffs varies from 0.1 percent in white potatoes to 70 percent in some nut kernels.More than 90 percent of the fat recovered in the world is obtained from about 20 species of plants and animals. Most of this separated fat is used eventually as human food. Consequently, fat technology deals largely with the separation and processing of fats into forms acceptable to the various dietary customs in the countries in which they are to be used. Chemically speaking, fats are triglycerides, uncharged esters of the three-carbon alcohol glycerol that are solid at room temperature (20° C). Triglycerides that are liquid at room temperature are referred to as oils. Triglycerides belong to a diverse class of biological molecules called lipids, which are generally water-insoluble but highly soluble in organic solvents.Known primarily as efficient energy stores in animals, triglycerides can be mobilized to meet the energy needs of the organism. Some plant species, such as avocados, olives, and nuts, have substantial amounts of triglycerides in seeds or fruits that serve as energy reserves for the next generation.However, triglycerides play a variety of biological roles. Concentrated fat deposits in adipose tissue insulate organs against shock and help to maintain a stable body temperature. Fat-soluble vitamins are involved in activities ranging from blood clotting to bone formation and can only be digested and transported when bonded to triglycerides.The consumption of fats in the diet requires personal responsibility and discipline, as there is diversity in the health impacts of different triglycerides.