Conjugated linoleic acid (hereinafter referred to as CLA) is a general term for a mixture of all stereoisomers and positional isomers of linoleic acid, which can be regarded as secondary derivatives of linoleic acid, with the molecular formula C17H31COOH. The double bonds of conjugated linoleic acid can be located at positions 7?9, 8?10, 9?11, 10?12, 11?13 and 12?14. Each double bond exists in two conformations: cis (c) and trans (t). Theoretically, there are more than 20 CLA isomers, among which c?9, t?11 and t?10, c?12 are the two most abundant ones.

Conjugated linoleic acid is absorbed through the digestive tract from food into the bloodstream and distributed throughout the body. After absorption, CLA is mainly incorporated into structural lipids of tissues. Part of CLA enters plasma phospholipids and cell?membrane phospholipids, or is metabolized in the liver to arachidonic acid, which is further synthesized into eicosanoid bioactive substances.