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Food Lipids: Chemistry, Nutrition, and Biotechnology

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21<br />

Conjugated Linoleic Acids:<br />

<strong>Nutrition</strong> <strong>and</strong> Biology<br />

BRUCE A. WATKINS <strong>and</strong> YONG LI<br />

Purdue University, West Lafayette, Indiana<br />

I. INTRODUCTION<br />

Conjugated linoleic acids (CLAs) are a family of positional <strong>and</strong> geometric isomers<br />

of octadecadienoic acid (18:2). Double bonds in CLA are conjugated <strong>and</strong> not separated<br />

by a methylene group (—CH2—) as in linoleic acid (LA or 18:2n-6), an �-6<br />

essential fatty acid. The CLA isomers are found in many foods (1) but are predominant<br />

in products derived from ruminant sources (beef, lamb, <strong>and</strong> dairy) because of<br />

the process of bacterial biohydrogenation of polyunsaturated fatty acids (PUFAs) in<br />

the rumen (1–3).<br />

The highest concentrations of CLA in food are present in dairy products (4,5)<br />

<strong>and</strong> fat in the meats of lamb, veal calves, <strong>and</strong> cattle (6). In most cases, the cis-9,<br />

trans-11 isomer is the chief isomer of CLA found in food. Estimates of CLA intake<br />

range from 0.3 to 1.5 g/person/day <strong>and</strong> appear to be dependent on gender <strong>and</strong> the<br />

intake of food from animal <strong>and</strong> vegetable origins (4).<br />

Since the finding that CLAs isolated from grilled beef inhibited chemically<br />

induced cancer (7–9), numerous studies have been initiated to investigate the physical,<br />

biochemical, <strong>and</strong> physiological properties of CLA isomers. The growing body<br />

of literature on CLA suggests that these isomeric conjugated fatty acids possess<br />

potent biological activities that may benefit human health.<br />

II. CHEMISTRY<br />

The acronym CLA is used to describe a family of octadecadienoic acid (18:2) isomers<br />

that possess a pair of conjugated double bonds along the alkyl chain from carbon 2<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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