Milk Fatty Acids: Emerging Perspectives

Nutritional quality is an important determinant of consumer food choices due to the growing awareness of the association between diet and health. Milk fatty acid (FA) composition is a major component of nutritive value of dairy products, in addition of being associated with both their physical and organoleptic properties. The FA profile of milk can be significantly altered through feeding of cows, offering the flexibility to respond to consumer demands and public health recommendations. Strong evidence suggests that specific intermediates of ruminal biohydrogenation of PUFA inhibit the growth of different human cancer cell lines, slow the development of tumors, affect lipoprotein metabolism and immune function, and enhance lean body mass in animal models. Consequently, several studies have investigated the potential to alter distribution and concentration in milk fat of different isomers of ruminal biohydrogenation, such as conjugated dienes and trans octadecenoic acids. Also, as milk fat is a common component of the human diet, its enrichment with n-3 PUFA provides the opportunity to increase intake of these essential FA by the general population. However, dietary PUFA are extensively metabolized in the rumen. Protecting FA represents a major challenge in formulating feed supplements that will enhance the postruminal supply of n-3 PUFA. Feeding FA as Ca salts has been proposed as a way to provide such protection. Recent work in our laboratory has demonstrated that n-3 PUFA included in large particles of Ca salts are physically protected against ruminal biohydrogenation, which increases the efficiency of their transfer from diet to milk fat. Furthermore, dairy products are the main source of branched-chain FA (BCFA) in human diet. These FA are synthesized by ruminal microorganisms and are essential components of their lipid membranes. For humans, health benefits such as prevention of necrotizing enterocolitis, symptom attenuation of some neurological diseases, or anticarcinogenic properties have been associated with these bioactive molecules. A series of experiments carried out in our laboratory provided more insight into the effect of different physiological and nutritional factors on milk BCFA composition in dairy cows. These trials showed that milk fat concentrations of BCFA are affected by lactation stage as well as forage type, level of concentrate, and dietary lipid supplementation. In conclusion, milk fat contributes to human health in many important ways. Nutrition and management of dairy cows offers the possibility to adjust milk FA composition as our knowledge of individual and combined health effects of numerous milk FA develop.