fat
In the broadest sense, a mixture of lipids – chiefly triglycerides (lipids containing three fatty acid molecules linked to a molecule of glycerol). More specifically, the term refers to a lipid mixture that is solid at room temperature (20°C/68°F); lipid mixtures that are liquid at room temperature are called oils. The higher the proportion of saturated fatty acids in a mixture, the harder the fat. Fats and oils (lipids) are compounds made up of glycerol and fatty acids. Fats are insoluble in water. Boiling fats in strong alkali forms soaps (saponification).
Fats are essential constituents of food for many animals, with a calorific value twice that of carbohydrates. However, eating too much fat, especially fat of animal origin, has been linked with heart disease in humans, where excess fat is deposited in the walls of arteries and may cause heart attacks. In many animals and plants, excess carbohydrates and proteins are converted into fats for storage. Mammals and other vertebrates store fats in specialized connective tissues (adipose tissues), which not only act as energy reserves but also insulate the body and cushion its organs.
As a nutrient, fat serves five purposes: it is a source of energy (9 kcal/g); makes the diet palatable; provides basic building blocks for cell structure; provides essential fatty acids (linoleic and linolenic); and acts as a carrier for fat-soluble vitamins (A, D, E, and K). Indeed, fatty tissue in the body stores fat-soluble vitamins. Foods rich in fat are butter, lard, and margarine. Products high in monounsaturated or polyunsaturated fats are thought to be less likely to contribute to cardiovascular disease.
Digestion of fats in humans In digestion fats are broken down into glycerol and fatty acids by the enzyme lipase with the help of bile. Inside the body, fatty acids and glycerol are recombined to produce fat again. Fats are used in respiration to liberate energy, and may be stored as body fat in special tissue under the skin, around the thighs and buttocks, and internal organs. In humans, this fat acts mainly as an energy reserve, or to help to protect internal organs from mechanical damage. In a few mammals, for example whales, it acts as an insulator. |
Olestra Olestra, a calorie-free substance that mimics fat, but is not absorbed by the body, was approved as safe to eat by a US food advisory panel in November 1995. In Olestra the glycerol molecule has been replaced by sucrose. Olestra is made by heating soybean or cottonseed oil at high temperatures and a further manipulation of chemical structure. |
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