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An unsaturated fat is a fat or fatty acid in which there is at least one double bond within the fatty acid chain. A fatty acid chain is monounsaturated if it contains one double bond, and polyunsaturated if it contains more than one double bond. Where double bonds are formed, hydrogen atoms are eliminated. Thus, a saturated fat has no double bonds, has the maximum number of hydrogens bonded to the carbons, and therefore is "saturated" with hydrogen atoms. In cellular metabolism, unsaturated fat molecules contain somewhat less energy (i.e., fewer calories) than an equivalent amount of saturated fat. The greater the degree of unsaturation in a fatty acid (i.e., the more double bonds in the fatty acid) the more vulnerable it is to lipid peroxidation (rancidity). Antioxidants can protect unsaturated fat from lipid peroxidation. == Chemistry and nutrition == Double bonds may be in either a ''cis'' or a ''trans'' isomer, depending on the geometry of the double bond. In the ''cis'' isomer, hydrogen atoms are on the same side of the double bond, whereas, in the ''trans'' isomer, they are on opposite sides (see trans fat). Saturated fats are popular with manufacturers of processed foods because they are less vulnerable to rancidity and are, in general, more solid at room temperature than ''unsaturated'' fats. Unsaturated chains have a lower melting point, hence increasing fluidity of the cell membranes. Although both monounsaturated and polyunsaturated fats can replace saturated fat in the diet, trans unsaturated fats should be avoided. Replacing saturated fats with unsaturated fats helps to lower levels of total cholesterol and LDL cholesterol in the blood. Trans unsaturated fats are particularly risky because the double bond stereochemistry allows the fat molecules to assume a linear conformation, which leads to efficient packing (i.e., plaque formation). The geometry of the cis double bond introduces a bend in the molecule, thereby precluding stable formations (see links above for drawings that illustrate this). Natural sources of fatty acids (see above) are rich in the cis isomer. Although polyunsaturated fats are protective against cardiac arrhythmias, a study of post-menopauseal women with a relatively low fat intake showed that polyunsaturated fat is positively associated with progression of coronary atherosclerosis, whereas monounsaturated fat is not. This probably is an indication of the greater vulnerability of polyunsaturated fats to lipid peroxidation, against which vitamin E has been shown to be protective. Examples of unsaturated fats are palmitoleic acid, oleic acid, myristoleic acid, linoleic acid, and arachidonic acid. Foods containing unsaturated fats include avocado, nuts, and vegetable oils such as canola and olive oils. Meat products contain both saturated and unsaturated fats. Although unsaturated fats are conventionally regarded as 'healthier' than saturated fats,〔(Fats and sugars ). BBC Health, retrieved 2013-04-07〕 the United States Food and Drug Administration (FDA) recommendation stated that the amount of unsaturated fat consumed should not exceed 30% of one's daily caloric intake. Most foods contain both unsaturated and saturated fats. Marketers advertise only one or the other, depending on which one makes up the majority. Thus, various unsaturated fat vegetable oils, such as olive oils, also contain saturated fat. In chemical analysis, fatty acids are separated by gas chromatography of methyl esters; additionally, a separation of unsaturated isomers is possible by argentation thin-layer chromatography.〔B. Breuer, T. Stuhlfauth et H. P. Fock, Separation of fatty acids or methyl esters including positional and geometric isomers by alumina argentation thin-layer chromatography, J. of Chromatogr. Science 25 (1987), S. 302–306 ()〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Unsaturated fat」の詳細全文を読む スポンサード リンク
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