Conjugated linoleic acid (CLA) is abundant in the meat and milk of ruminants including cattle and sheep. This is attributed to linoleate isomerase produced by the anaerobic bacterium Butyrivibrio fibrisolvens residing in the intestinal tract of ruminants, which catalyzes the conversion of linoleic acid to conjugated linoleic acid predominantly in the form of the c-9,t-11 isomer. Therefore, natural CLA mainly occurs as a microbial metabolite generated within the digestive tract of ruminants.
Trace amounts of CLA can also be found in the tissues, blood and body fluids of other animals. Plant-derived foods contain low levels of CLA as well, yet their isomer profiles differ significantly from those of animal-sourced products. In particular, the biologically active c-9,t-11 isomer exists at minimal concentrations in plant foods. Marine foods also contain only negligible levels of conjugated linoleic acid.