Conjugated linoleic acids : Variations of their concentrations in milk and dairy products

The Conjugated Linoleic Acids (CLA), particularly the c9t11-CLA and the t10c12-CLA, exhibit some remarkable biological properties : anticancerous and antiatherosclerosis effects, prevention of obesity for example. Although the greatest contents are found into milk and dairy products, their concentrations are still insufficient for obtaining beneficial effects. Several factors can modulate the CLA contents in milk and dairy products by enzyme regulation of the linoleic acid (C18:2) biohydrogenation pathway. A marked dietary supplementation by polyunsaturated fatty acids (especially C18:2 and linolenic acid), very acid pH in rumen, rapid emptying of the rumen and other local factors (copper, monensin) lower biohydrogenation, leading to accumulation of intermediates, CLA and trans-monoenoic acids, in rumen then in milk, instead of complete saturation into stearic acid. Although other factors related to animal and to industrial treatment of milk, diversely affect CLA concentrations in milk, feeding practices easily checked by farmers (dietary fat supplementation, forage utilisation) induce milk, and so dairy products, enrichment of milk, and so dairy products, by CLA. In conclusion, in these conditions, the mean daily CLA supply by man would become sufficient for allowing beneficial effects, notably anticancetons, on health.