In biochemistry, fat is a generic term for a class of lipids. Fats are produced by organic processes in animals and plants. All fats are insoluble in water and have a density significantly below that of water (i.e. they float on water.) Fats that are liquid at room temperature are often referred to as oil.
Most fats are composed primarily of triglycerides; some monoglycerides and diglycerides are mixed in, produced by incomplete esterification. These are extracted and used as an ingredient.
Products with a lot of saturated fats tend to be solid at room temperature, while products containing unsaturated fats, which include monounsaturated fats and polyunsaturated fats, tend to be liquid at room temperature.
Predominantly saturated fats (solid at room temperature) include all animal fats (e.g. milk fat, lard, tallow), as well as palm oil, coconut oil, cocoa butter and hydrogenated vegetable oil (shortening). All other vegetable fats, such as those coming from olive, peanut, maize (corn oil ), cottonseed, sunflower, safflower, and soybean, are predominantly unsaturated and remain liquid at room temperature. However, both vegetable and animal fats contain saturated and unsaturated fats. Some oils (such as olive oil) contain mainly monounsaturated fats, while others present quite a high percentage of polyunsaturated fats (sunflower, rape).
In the ancient Minoan culture, and in many of the other early Mediterranean cultures, olive oil was a very important commodity and at times used as a measure of wealth.
Different varieties of fat have seen, and indeed still see, much use as lubricants, although recently various synthetic substances and petroleum derivatives has taken over in most industrial applications.
In cooking, products with a high fat content are often used as enhancers of taste, for example butter, milk, cheese and other dairy products.
Animal fat or "drippings" are also used in the traditional cuisine of European countries. In Denmark pork fedt (the fat from the frying pan after the meat has been cooked) is drained and filtered to strain any large particles. It is then placed in a container and cooled down until solid. It can be kept for extremely long periods of time in a refrigerator. Often it is used as a more flavourful alternative to butter or margarine, and is easily spread even when cold.
In traditional Jewish cuisine the fat from chickens, known as schmaltz, is used.
Another use of fat in cooking is as heat conductor in frying.
Fats in nutrition
Fat is one of the three main classes of food and, at approximately 38 kJ (9 kilocalories) per gram, as compared to sugar with 17 kJ (4 kcal) per gram or ethanol with 29 kJ (7 kcal) per gram, the most concentrated form of metabolic energy available to humans. (Note that 1 kcal = 1 "Calorie", capitalised in nutrition-related contexts.) Vitamins A, D, E, and K are fat-soluble meaning they can only be digested, absorbed, and transported in conjunction with fats. Fats are sources of essential fatty acids, an important dietary requirement.
They also serve as energy stores for the body. In food, there are two types of fats: saturated and unsaturated. Fats are broken down in the body to release glycerol and free fatty acids. The glycerol can be converted to glucose by the liver and thus used as a source of energy. The fatty acids are a good source of energy for many tissues, especially heart and skeletal muscle.
The biological imperative
All varieties of fat have an extraordinary energy content. In animals, fat acts as an energy reserve, and is stored in fatty tissue, normally located subcutaneously or surrounding organs. Fatty tissue consist of fat cells, designed to store energy in the form of fat.
Energy is stored as fatty tissue when the nutrition/energy content of the blood remains higher than is consumed by muscular and other activity. When the energy content in the blood lessens, the fatty tissue reacts by releasing a corresponding amount of energy from the fat cells. This activity is controlled by insulin and other hormones in the body.
Adipose, or fatty, tissue is the human body's means of storing metabolic energy over extended periods of time. The location of the tissue determines its metabolic profile: "visceral fat" (around the abdomen) is prone to lead to insulin resistance, while "peripheral fat" (around the limbs) is much more harmless.
See the main article on fatty acid metabolism
The metabolism of lipids is a closely regulated system in virtually all lifeforms. It is effected by a variety of enzymes and, in higher organisms, regulated by hormones. Research is ongoing on the relative influence of various hormonal regulators on the anabolism (production) and catabolism (breakdown, also termed lipolysis) of fatty molecules.
A subject of particularly close study is cholesterol, which is a fatty substance best known for its role in development of atherosclerosis.