Kritchevsky D
Wistar Institute, Philadelphia, PA 19104, USA.
Br J Nutr. 2000 May;83(5):459-65.
Conjugated linoleic acid (CLA) is a collective term for positional and geometric isomers of octadecadienoic acid in which the double bonds are conjugated, i.e. contiguous. CLA was identified as a component of milk and dairy products over 20 years ago. It is formed as an intermediate in the course of the conversion of linoleic acid to oleic acid in the rumen. The predominant naturally occurring isomer is the cis-9, trans-11 modification. Treatment of linoleic acid-rich oils such as safflower oil, soybean oil, or maize oil with base and heat will result in the formation of CLA. Two isomers predominate in the synthetic preparation, c9,t11 and t10,c12. CLA has been shown to inhibit chemically-induced skin, stomach, mammary or colon tumours in mice and rats. The inhibition of mammary tumours in rats is effective regardless of type of carcinogen or type or amount of dietary fat. CLA has also been shown to inhibit cholesterol-induced atherosclerosis in rabbits. When young animals (mice, pigs) are placed on CLA-containing diets after weaning they accumulate more body protein and less fat. Since CLA is derived from the milk of ruminant animals and is found primarily in their meat and in products derived from their milk there is a concerted world-wide effort to increase CLA content of milk by dietary means. Its effect on growth (less fat, more protein) is also a subject of active research. The mechanisms underlying the effects of CLA are still moot.
共轭亚油酸（CLA）是十八碳二烯酸的位置和几何异构体的统称，其中双键是共轭的，即相邻的。20多年前，CLA被确定为牛奶和乳制品的一种成分。它是瘤胃中亚油酸转化为油酸过程中的一种中间产物。天然存在的主要异构体是顺式-9，反式-11构型。用碱和热处理富含亚油酸的油，如红花油、大豆油或玉米油，会导致CLA的形成。在合成制剂中，两种异构体占主导地位，即c9,t11和t10,c12。已证明CLA能抑制化学诱导的小鼠和大鼠皮肤、胃、乳腺或结肠肿瘤。对大鼠乳腺肿瘤的抑制作用不受致癌物类型或膳食脂肪类型及含量的影响。CLA还被证明能抑制兔子的胆固醇诱导的动脉粥样硬化。当幼小动物（小鼠、猪）断奶后食用含CLA的日粮时，它们会积累更多的身体蛋白质和更少的脂肪。由于CLA来源于反刍动物的乳汁，主要存在于它们的肉和奶制品中，因此全世界正在齐心协力通过饮食手段提高牛奶中的CLA含量。它对生长的影响（脂肪减少，蛋白质增加）也是一个积极研究的课题。CLA作用的潜在机制仍有争议。
