Conjugated Linoleic Acid: A Milk Fatty Acid with Unique Health Benefit Properties

Abstract

Human diet comprises of milk and milk products in both developed and developing parts of globe. Milk fat is the major energy source in Indian diet but due to the fear of hypercholesterolemia, saturated fats have lead to avoidance of dietary fats especially of animal origin. However, milk contains a number of components with beneficial properties, one such compound associated with the fat phase is Conjugated Linoleic Acid (CLA) which has potential health benefits towards human beings. Conjugated Linoleic Acid (CLA) refers to a mixture of positional and geometric isomers of linoleic acid (cis-9, cis-12, C18:2) with two conjugated double bonds at various carbon positions in the fatty acid chain. It is formed as an intermediate during the biohydrogenation of linoleic acid by linoleic acid isomerase from the rumen bacteria Butyrivibrio fibrisolvens (Kritchevsky, 2000) or from the endogenous conversion of trans-11, C18:1 (Transvaccenic Acid) another intermediate of linoleic or linolenic acid biohydrogenation by ∆9-desaturase in the mammary gland (Corl et al., 2001). Milk fat is the richest natural dietary source of CLA. Milk contains an average 4.5mg CLA/g of fat (Kelly et al., 1998). Recent studies have shown that the CLA content of milk fat can be markedly enhanced by dietary manipulation especially those involving dietary addition of plant oils which are high in unsaturated fatty acids (Griinari and Bauman, 1999). Dietary increase of linoleic acid (C18:2) and linolenic acid (C18:3) is one of the feeding strategies for increasing the CLA concentration in milk which is the main precursor of CLA. The main sources of linoleic acid for feeding animals are cereals, oil seeds, oils etc (Kelly et al., 1998) There is an increasing research interest towards the CLA and its potential health benefits such as anticarcinogenic, antiatherogenic, antidiabetic and immunomodulatory effects (Belury, 2002; Tyagi and kathirvelan, 2006). The potential anti-cancer effect of CLA is well documented, with the majority of experimental work conducted in vitro or in animal models (Ip et al., 1994). It has been demonstrated that CLA has the ability to affect mammary cancer, stomach cancer, skin cancer and prostate cancer. Most of the anticarcinogens are of plant origin but CLA is unique, it is present in food from animal sources and its anti-cancer efficacy is expressed at concentrations close to human consumption level. The unique structural and functional properties of CLA appear to modulate cellular process involved in carcinogenesis.