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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.

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Chemical composition 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 fat 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 in majority monounsaturated fats, while others present quite a high percentage of polyunsaturated fats (sunflower, rape).

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.

Utilization 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 has 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. Another use of fat in cooking is as heat conductor in frying.

Fat as food Fat is one of the three main classes of food and, at approximately 38 kJ (9 Cal) per gram, as compared to sugar with 17 kJ (4 Cal) per gram or ethanol with 29 kJ (7 Cal) per gram, the most concentrated form of metabolic energy[?] available to humans. Vitamins A, D and E are fat soluable and occur only 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.

In the modern world, excess fatty tissue on a human is often considered an aesthetic and medical problem. For a discussion of this, see dieting and obesity. In earlier times and other societies, fat was considered aesthetically pleasing. Rembrandt's and especially Peter Paul Rubens's paintings, giving us the term Rubenesque, to describe a large woman. Fat, depending on the age and culture, is considered at once a sign of wealth, power, prestige, gluttony, and sloth.

See also: Carbohydrate; protein; lipid; biodiesel.

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