CLA refers to a series of positional and stereoisomers of linoleic acid (LA), also known as octadecadienoic acid. CLA occurs naturally in beef and dairy products (also meat and milk products from other ruminants) as a result of bacterial hydrogenation of LA in the rumen. Over the past two decades, CLA has emerged as an important class of polyunsaturated fatty acids because of the growing number of its apparently beneficial effects for human health. Interestingly, CLA was first discovered during an investigation into the health risks of grilled beef, with the aim of identifying potentially carcinogenic components. To the surprise of the scientists carrying out this study, the fatty acids isolated from beef had anti-carcinogenic properties instead. These initial findings have since been expanded and continued by a number of laboratories around the world, revealing through animal and in vitro studies that CLA exerts its effects on several different types of cancer. Just as importantly, CLA has been shown to exhibit a variety of additional biomedical properties, including anti-adipogenic, anti-atherogenic, anti-diabetogenic, and anti-inflammatory activities.

An informative review summarising the many health-related findings for CLA was recently published in the Journal of Nutritional Biochemistry by a team of scientists led by Gabriel Fernandes of the University of Texas Health Science Center in San Antonio. One key aspect highlighted by this review and which has emerged from several recent studies is the variation in bioactivities between the different isomers of CLA. In most cases, commercially available CLA is an equal mixture of cis-9, trans-11 (c9t11) and trans-10, cis-12 (t10c12) isomers with several other minor components. It now appears, for example, that t10c12 is solely responsible for the anti-adipogenic effects of CLA. In other instances, c9t11 and t10c12 have been shown to act in either an opposing or an additive manner, depending upon the cellular or physiological context. Because of this functional complexity, it could be useful for manufacturers to more carefully define the isomeric composition of CLA in foods and beverages, and to associate health claims with those CLA isomers known to be present at bioactive levels.

Since the publication of this review, several other primary research articles have been published which examine the biomedical utility of CLA. One of these recently appeared in the British Journal of Nutrition, and addresses the question of body fat mass (BFM) reduction induced by CLA. Led by Jean-Michel Gaullier of Link Medical Research in Norway, the study reports that in healthy but overweight or obese adults, a 6-month supplementation with CLA results in an increase in lean body mass (LBM) and a concomitant reduction in BFM. This fat loss occurs primarily in women and is region-specific. Another study, led by Susan Steck of the University of North Carolina and recently published in the May 2007 issue of the Journal of Nutrition, also revealed an increase in LBM in obese humans whose diets were supplemented with CLA for only 12 weeks.

These and numerous other research studies provide the basis for the apparent health benefits of CLA, although some potential side effects have also been reported. Over the coming years, it will be important for manufacturers to carefully monitor research trends in this area, and to respond quickly to growing consumer awareness of this functional ingredient.

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