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Kraft Foods, Inc., Chicago (J.A.S.), Illinois
National Dairy Council, Rosemont (G.D.M.), Illinois
Address reprint requests to: Gregory D. Miller, Ph.D., National Dairy Council, O’Hare International Center, 10255 W. Higgins Rd., Suite 900, Rosemont, IL 60018-5616. gregorym{at}rosedmi.com.
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INTRODUCTION |
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 TOP INTRODUCTION REFERENCES |
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Presently, CLA is a term used to denote a group of isomers of linoleic acid (cis-9, cis-12-octadecadienoic acid). The characteristic that binds these isomers together is that, unlike linoleic acid, the two double bonds along the 18-carbon fatty acid chain are not separated by a methylene carbon and, hence, are termed "conjugated." Of the many positional and geometric isomers of CLA that are possible, the cis-9, trans-11-octadecadienoic acid isomer predominates in food products [1]. This isomer is naturally rich in milk fat, being produced by rumen bacteria during the process of biohydrogenation. The reader is encouraged to read Griinari and Bauman [2] for a review of the biosynthesis of CLA.
The history of conjugated linoleic acid extends back to the 1930s, when the presence of fatty acids obtained from butter fat was reported to exhibit spectrophotometric absorption at 230 µm, thus indicating the presence of two conjugated double bonds. It was not until the advent of gas liquid chromotography, that Peter Parodi and others were able to fractionate the methyl esters of milk fat and hence were able to quantitatively determine some of the isomers of CLA, including the cis-9, trans-11-octadecadienoic acid isomer, which has the proposed name of rumenic acid. For an excellent historical summary of the discovery of CLA in milk fat, the reader is referred to a review by Parodi [3].
The turning point in CLA research can be traced back to investigations by Michael Pariza that revealed the presence of "mutagenesis inhibitory" activity in extracts of grilled ground beef [4]. Subsequent research established that the extract exhibited anticarcinogenesis activity as well [5] and that the identity of the active principle was CLA [6]. These studies have led to hundreds of investigations and the recognition of multiple biological effects of CLA. The symposium organizers selected five areas of CLA research to highlight in the symposium: inhibition of mammary cancer, retardation and regression of atherosclerosis, modification of body fat metabolism and partitioning, anti-diabetic effect and enhancement of bone formation.
This supplemental section includes three of the five papers presented at the symposium. Not included in the supplement are papers by Drs. Clement Ip and Karen Houseknecht. Both investigators have recently published papers that include much of the material they presented during the symposium. Clement Ip’s presentation focused on research which demonstrated for the first time that naturally-occurring CLA in a food form had biological activity and that this activity was similar to that produced by a mixture of CLA isomers delivered as free fatty acids [7]. Karen Houseknecht’s research extends to the original observation of an anti-diabetic effect by dietary CLA using the Zucker diabetic fatty rat model [8], and her presentation included research that was recently published on the mode of action(s) by which CLA was responsible for the anti-diabetic effect [9–11].
The first of the papers in this supplement is by David Kritchevsky and contains research that examined the effect of CLA on the establishment and progression of atherosclerosis in rabbits. It is interesting to note that Dr. Kritchevsky’s research provides evidence that not all trans fatty acids may similarly contribute to cardiovascular disease. The next paper is authored by Drs. Bruce Watkins and Mark Seifert and reviews bone biology and the effects of dietary factors such as CLA on bone metabolism. The last paper is by Dr. James DeLany and colleagues and examines changes in body composition with CLA consumption.
The supplement editors hope that the reader of this supplement finds the information interesting and is able to gain a better understanding of the potential human health benefits of consuming diets high in CLA.
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FOOTNOTES |
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REFERENCES |
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TOPINTRODUCTIONREFERENCES |
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This article has been cited by other articles:
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  G. D. Miller, J. K. Jarvis, and L. D. McBean The Importance of Meeting Calcium Needs with Foods J. Am. Coll. Nutr., April 1, 2001; 20(2): 168S - 185. [Abstract] [Full Text] [PDF]
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