Conjugated linoleic acid Dietary sources

Another important dietary source of trans fat is conjugated linoleic acid, a class of compounds collectively known as CLA. Many CLA isomers contain conjugated cis/trans and trans/trans double bonds. Interest in CLA research has increased significantly in the past few years because several cis/trans CLA isomers have been reported to exhibit different beneficial physiological effects in animal studies (Yurawecz et al., 1999). The reader is referred to a collection of analytical papers published in a dossier (Mossoba, 2001, and references therein) that details several chromatographic and spectroscopic techniques and procedures that have been successfully applied to CLA analysis. 

Chouinard, P.Y., Corneau, L., Butler, W.R., Chilliard, Y., Drackley, J.K., Bauman, D.E. 2001. Effect of dietary lipid source on conjugated linoleic acid concentrations in milk fat. J. Dairy Sci. 84, 680-690. 

Kelly, M.L., Berry, J.R., Dwyer, D.A., Griinari, J.M., Chouinard, P.Y., Van Amburgh, M.E., Bauman, D.E. 1998a. Dietary fatty acid sources affect conjugated linoleic acid concentrations in milk from lactating dairy cows. J. Nutr. 128, 881-885. 

Conjugated linoleic acid (CLA) is naturally present in milk, dairy products, and the meat of ruminants (1). Ruminants are the major dietary source of this fatty acid because of the unique abihty of rumen bacteria to convert linoleic acid into cis-9,trans- CLA (c9,tll-CLA) (1). This reaction is part of a process that takes place in the rumen it is called biohydrogenation and it converts linoleic acid [or, less efficiently, other 18-carbon polyunsaturated fatty acids (PUFA) with double bonds located at 9 and 12 positions] to stearic acid (1). During this process, vaccenic acid (tl 1-18 1) is formed. This acid can be converted to CLA in all organisms that possess A9-desaturase (2). 

M. E., and Bauman D.E. (1998) Dietary Fatty Acid Sources Affect Conjugated Linoleic Acid Concentrations in MiUc from Lactating Dairy Cows, J. Nutr. 128, 881-885. 

Twibell, R.G., Watkins, B.A., and Brown, P.B. (2001) Dietary Conjugated Linoleic Acids and Lipid Source Alter Fatty Acid Composition of Juvenile Yellow Perch, Perea flavescens, J. Nutr. 131, 2322-2328. 

Wachira, A. M., Sinclair, L. A., Wilkinson, R. G., Enser, M., Wood, J. D., Eisher, A. V. (2002). Effects of dietary fat source and breed on the carcass composition, n-3 polyunsaturated fatty acid and conjugated linoleic acid content of sheep meat and adipose tissue. British Journal of Nutrition, 88, 697-709. 

McGuire, M.K., McGuire, M.A., Ritzenthaler, K.L., and Schultz, T.D. 1999. Dietary sources and intakes of Conjugated Linoleic acid in take in humans. In Advances in Conjugated Linoleic Acid research, pp. 369-377 [Yurawecz, M.P., Mossoba, M.M., Kramer, J.K.G., P.M.W., and Nelson, G. eds] Champaign AOCS Press. 

CLA refers to a mixture of positional and geometric isomers of linoleic acid (cis-9, cis-12 octadecadienoic acid) with a conjugated double bond system. The structure of two CLA isomers is contrasted with linoleic and vaccenic acids in Figure 3.1. The presence of CLA isomers in ruminant fat is related to the biohydrogenation of polyunsaturated fatty acids (PUFAs) in the rumen. Ruminant fats are relatively more saturated than most plant oils and this is also a consequence of biohydrogenation of dietary PUFAs by rumen bacteria. Increases in saturated fatty acids are considered undesirable, but consumption of CLA has been shown to be associated with many health benefits, and food products derived from ruminants are the major dietary source of CLA for humans. The interest in health benefits of CLA has its genesis in the research by Pariza and associates who first demonstrated that... 

Chin, S. E, Liu, W., Storkson, J. M., Ha, Y. L., and Pariza, M. W. 1992. Dietary sources of conjugated dienoic fatty acids of linoleic acid, a newly recognized class of anticarcinogens. J. Food Comp. Anal., 5,185-197. 

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