What is CLA?
The conjugated linoleic acid (CLA) is a mixture of positional and geometric isomers of linoleic acid, a fatty acid (or fat in plain English). CLAs have two conjugated (alternate) unsaturated double bonds at various carbon positions in the fatty acid chain. Each double bond can be a cis or trans, but those with one trans double bond are bioactive. CLAs are synthesized by the rumen microbes, primarily Butyrivibrio fibrisolvens, which is to say those present in the rumen of cows, sheep, goats, and buffaloes among the domestic animals.
Why is CLA important?
Ever since Ha and his coworkers1 demonstrated that CLA obtained from fried ground beef inhibited carcinogenesis, a whole new era of research dedicated to CLA began. Thanks to thousands of reports, principally based on in vitro, microbial, animal and of late clinical trials on humans, CLA is now linked to have beneficial effects in obesity, diabetes, cardiovascular disease, cancer, and atherosclerosis. The CLA has also been shown to have immunomodulatory, apoptotic and osteosynthetic effects. More recently, FDA approved the CLA as Generally Recognized as Safe category so that it can be used in various food and beverages. This may open up yet another era on CLA research aimed at finding some important solutions to ever increasing problems of aforementioned chronic diseases. On the other hand, a few negative effects of CLA have also been reported, such as fatty liver and spleen, induction of colon carcinogenesis and hyperproinsulinemia. While a plethora of research have shown the positive effects of CLA in many experimental models, it is by no means a surefire finding in actual human beings under practical situations. Moreover, its mechanism of action is also not very clear. As a result, scientists are conducting numerous experiments every year to provide a definite answer as to the great positive effects of CLA in humans and its mode of action.
Where can CLA be found?
Since only the microbes present in the rumen are capable of actually synthesizing the CLA or its precursor trans-vaccenic acid, another type of fat, foods of ruminant origin are the primary sources of CLA for human consumption. However, milk or meat from animals grazed on fresh pastures has the highest concentrations of CLA (does it sound organic? I bet it does). Increasing the proportion of grass in animal diet would also help increase the CLA content in the milk or meat. However, milk or meat from animals fed large amounts of grains, such as those in the form of total mixed rations or beef fattening programs have the least amount of CLA. Trans-vaccenic acid can be converted into CLA in the mammary gland with the help of an enzyme, thus enhancing the overall CLA content of foods from ruminants.
1Ha, Y. L., N. K. Grimm and M. W. Pariza. 1987. Anticarcinogens from fried ground beef: Heat-altered derivatives of linoleic
acid. Carcinogenesis. 8:1881-1887.
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