unsaturated fat: see saturated fat.

saturated fat, any solid fat that is an ester of glycerol and a saturated fatty acid. The molecules of a saturated fat have only single bonds between carbon atoms; if double bonds are present in the fatty acid portion of the molecule, the fat is said to be unsaturated. Unsaturated fats generally have lower melting points than saturated fats and are often liquids (oils) at room temperature. Unsaturated fats can be converted to saturated fats by a process called hydrogenation; since this usually raises the melting point of the fat and makes it a solid, the process is also called hardening. A correlation has been found between the consumption of solid fats in food and cholesterol levels in blood. Cholesterol forms arterial plaques that may lead to blockage of the arteries, i.e., atherosclerosis. Dietary guidelines in the United States call for reduced intake of saturated fat. See fats and oils.

fat substitute, substance used to replace dietary fat in the manufacture of foods. Fat substitutes are made in a variety of ways, mostly by manipulating natural food products such as egg whites, whey, and oats. Fat substitutes try to mimic the texture and flavor of fat while providing fewer calories and less metabolizable fat. The dietary consequences of consuming fat substitutes are under scrutiny.

fat: see fats and oils; obesity.

Charles the Fat, French king: see Charles III, emperor of the West.

or fatty tissue

Connective tissue consisting mainly of fat cells, specialized to synthesize and contain large globules of fat, within a structural network of fibres. It is found mainly under the skin but also in deposits between the muscles, in the intestines and in their membrane folds, around the heart, and elsewhere. The fat stored in this tissue comes from dietary fats or is produced in the body. It acts as a fuel reserve for times of starvation or great exertion, helps conserve body heat, and forms pads between organs.

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Any organic compound of plant or animal origin that is not volatile, does not dissolve in water, and is oily or greasy. Chemically, fats are identical to animal and vegetable oils, consisting mainly of triglycerides (esters of glycerol with fatty acids). Fats that are liquid at room temperature are called oils. Differences in melting temperature and physical state depend on the saturation of the fatty acids and the length of their carbon chains. The glycerides may have only a few different component fatty acids or as many as 100 (in butterfat). Almost all natural fats and oils incorporate only fatty acids that are constructed from two-carbon units and thus contain only even numbers of carbon atoms. Natural fats such as corn oil have small amounts of compounds besides triglycerides, including phospholipids, plant steroids, tocopherols (vitamin E), vitamin A, waxes, carotenoids, and many others, including decomposition products of these constituents. Sources of fats in foods include ripe seeds and some fruits (e.g., corn, peanuts, olives, avocados) and animal products (e.g., meat, eggs, milk). Fats contain more than twice as much energy (calories) per unit of weight as proteins and carbohydrates. Digestion of fats in foods, often partial, is carried out by enzymes called lipases. The breakdown products are absorbed from the intestine into the blood, which carries microscopic fat droplets reconstituted from digested fats (or synthesized in cells) to sites of storage or use. Fats are readily broken down—primarily into glycerol and fatty acids—by hydrolysis, a first step for many of their numerous industrial uses. Seealso lipid.

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known as Charles the Fat

(born 839, Bavaria? [Germany]—died Jan. 13, 888, Neidingen) Frankish king and emperor (881–87). The great-grandson of Charlemagne, he inherited the kingdoms of Swabia (876) and Italy (879). Charles was crowned emperor by the pope in 881. He gained control of the eastern and western Frankish kingdoms on the deaths of their rulers, and by 885 he had reunited all of Charlemagne's empire except Provence. Chronically ill, he failed to attack the Saracens and used tribute to buy off Viking invaders. His nephew Arnulf led an uprising against him in 887, and his fall marked the final disintegration of the empire of Charlemagne.

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