Conjugated Linoleic Acid

Conjugated linoleic acids (CLA) are a family of isomers of linoleic acid. In principle, 28 isomers are possible. CLA is found mostly in the meat and dairy products derived from ruminants. The two C=C double bonds are conjugated (i.e., separated by a single bond) as opposed by "typical" polyunsaturated fatty acids where double bonds are separated by two single bonds. CLAs are simultaneously both cis-fats and trans-fats, as one of the two C=C bonds is ''cis'' and the other ''trans''.

CLA is naturally present in milkfat and beef, has shown some potentially beneficial effects on rodent models of cardiometabolic disease, and is also available as a dietary supplement.

Biochemistry

CLA describes a variety of isomers of octadecadienoic fatty acids.

Commonly, CLAs are studied as some mixture of isomers wherein the isomers c9,t11-CLA (rumenic acid) and t10,c12-CLA were the most abundant. Studies show however that individual isomers have distinct health effects.

Conjugated linoleic acid is both a ''trans'' fatty acid and a ''cis'' fatty acid. The ''cis'' bond causes a lower melting point and, ostensibly, also the observed beneficial health effects. Unlike other ''trans'' fatty acids, it may have beneficial effects on human health. CLA is conjugated, and in the United States, ''trans'' linkages in a conjugated system are not counted as ''trans'' fats for the purposes of nutritional regulations and labeling. CLA and some ''trans'' isomers of oleic acid are produced by microorganisms in the rumens of ruminants. Non-ruminants, including humans, produce certain isomers of CLA from ''trans'' isomers of oleic acid, such as vaccenic acid, which is converted to CLA by delta-9-desaturase.

In healthy humans, CLA and the related conjugated linolenic acid (CLNA) isomers are bioconverted from linoleic acid and alpha-linolenic acid, respectively, mainly by '' Bifidobacterium'' bacteria strains inhabiting the gastrointestinal tract. However, this bioconversion may not occur at any significant level in those with a digestive disease, gluten sensitivity, or dysbiosis.

Health effects

CLA is marketed in dietary supplement form for its supposed anti-cancer benefit (for which there is a lack of robust evidence or well-accepted mechanism, and very few studies conducted so far) and as a bodybuilding aid. A 2004 review of the evidence said that while CLA seemed beneficial in animal models, there was a lack of good evidence for health benefits in humans despite the many claims made for CLA supplementation.

Likewise, there is insufficient evidence that CLA has a useful benefit for overweight or obese people, as it has been found to have no long-term effect on body composition. Although CLA has shown an effect on insulin response in diabetic rats, there is currently no evidence of this effect in humans.

Dietary sources

Food products from grass-fed ruminants (e.g. mutton and beef) are good sources of CLA and contain much more of it than those from grain-fed animals. Eggs from chickens that have been fed CLA are also rich in CLA, and CLA in egg yolks has been shown to survive the temperatures encountered during frying. Some mushrooms, such as ''Agaricus bisporus'' and '' Agaricus subrufescens'', are rare non-animal sources of CLA.

However, dietary punicic acid—which is abundant in pomegranate seeds—is converted to the rumenic acid (which is 9Z11E-CLA) upon absorption in rats, suggesting that non-animal sources can still effectively provide dietary CLA.

History

In 1979 CLAs were found to inhibit chemically-induced cancer in mice and research on its biological activity has continued.

In 2008, the United States Food and Drug Administration categorized CLA as generally recognized as safe (GRAS).

See also

* Conjugated fatty acids

References

{{DEFAULTSORT:Conjugated Linoleic Acid
Aromatase inhibitors
Dietary supplements
Fatty acids