Conjugated linoleic acid (CLA) is a naturally occurring fatty acid that is produced by a bio-hydrogenation process in the rumen, and thus is present in dairy products and ruminant meat. CLA includes 28 positional and geometrical isomers, of which only 9cis, 11trans and 10trans, 12cis have thus far been proven to possess biological activities, demonstrated in a wide range of animal models, such as anti-obesity, antiatherogenic, anticarcinogenic activities and to modulate immune functions. A common mechanism by which CLA could exert its beneficial effects may be re-conducted at least in part to its metabolism and consequent perturbation of fatty acid metabolism.

CLA is desaturated and elongated, keeping the conjugated diene structure, to conjugated linolenic (CD18:3), conjugated eicosatrienoic (CD 20:3) and conjugated arachidonic acid (CD20:4), sharing the same enzyme system used by linoleic acid. As a consequence, CLA seems to inhibit desaturation and elongation of linoleic acid, decreasing the accumulation of linoleic acid metabolites that are replaced by CLA metabolites, which have been shown to be powerful inhibitors of lipoxygenase and cycloxygenase.

Furthermore, other metabolites, conjugated 16:2 and 16:3, deriving most probably from peroxisomal beta oxidation of CLA and its metabolites respectively, have been detected. Their formation may implicate that CLA is  a  good  ligand  in  vivo  for  peroxisome  proliferator activated receptors (PPARs). These receptors, which molecular assays have indeed indicated that CLA is a high affinity ligand, belong to a family of transcription factors known to affect gene expression and thereby glucose and lipid metabolism.

We have shown that CLA metabolism follows a similar pattern in different animal species such as rodents, turkeys, dogs and humans. However some differences were detected in terms of accumulation of metabolites in plasma which may reflect differences in fatty acid metabolism in these species.