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c9, t11 conjugated linoleic acid
IUPAC name	(9Z,11E)-octadeca-9,11-dienoic acid
Other names	Bovinic acid, Rumenic acid
Identifiers
CAS number	2420-56-6
PubChem	5280644
SMILES	CCCCCCC=CC=CCCCCCCCC(=O)O
Properties
Molecular formula	C18H32O2
Molar mass	280.44548
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

Conjugated linoleic acids (CLA) are a family of at least 28^[1] isomers of linoleic acid found especially in the meat and dairy products derived from ruminants. As the name implies, the double bonds of CLAs are conjugated.

Contents 1 History 2 Biochemistry 3 Diet and health 3.1 Possible adverse effects of CLA in humans 3.2 Dietary Sources 4 See also 5 References 5.1 General references

[edit] History

CLAs were discovered accidentally by researchers looking for mutagens in beef. In 1979, researchers from the University of Wisconsin applied a beef extract to mice skin. The mice were then exposed to a strong carcinogen (isolated from tobacco). When the researchers counted the number of tumors developed by the mice 16 weeks later, they found, to their surprise, that the mice exposed to the beef extract had 20 % fewer tumors. The identity of this anti-carcinogen was not discovered till almost a decade later in 1987. Micheal Pariza, the scientist who discovered CLA, later remarked that "few anticarcinogens, and certainly no other known fatty acids, are as effective as CLA in inhibiting carcinogenesis in these models." ^{[2] [3]}

[edit] Biochemistry

Most studies of CLAs have used a mixture of isomers wherein the isomers c9, t11-CLA and t10, c12-CLA were the most abundant ones.^[4]

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 is not harmful, but beneficial.^[5] 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.^[6][7]

[edit] Diet and health

Antioxidant and anti-cancer properties have been attributed to CLA, and studies on mice and rats show encouraging results in hindering the growth of tumors in mammary, skin, and colon tissues.^{[8][9][10][11][12][13][14][15][16] [17] [18][19][20][21][22]} It has been reported that CLA can up-regulate the tumor suppressor gene PTPRG, and may have anti cancer properties.^[23][9]

A European team led by the Swiss scientist Lukas Rist has found that mothers consuming mostly organic milk and meat products have about 50 percent higher levels of rumenic acid in their breast milk.^[24]

Some studies of CLA in human diets show that it may reduce body fat,^[25] , especially abdominal fat. A maximum reduction in body fat was achieved with a daily dose of 3.4g.^[26] However,experts do not recommend taking CLA supplements. CLA supplements contain high levels of the t10,c12 CLA isomer, which has been linked to multiple side effects.^[27] Supplementation with this form of CLA has been shown to increase C-reactive protein levels, possibly to induce oxidative stress,^[28] to reduce insulin sensitivity, and to increase lipid peroxidation.^[29] However, the significance of these findings is unknown, and other studies suggest that CLA may protect cells from oxidative damage by increasing glutathione levels without inducing lipid peroxidation.^[30] It is possible, however, that the observation of markers of increased lipid oxidation may indicate potentially desirable lipolytic effects. Further studies are necessary to establish the clinical significance of such observations.

[edit] Possible adverse effects of CLA in humans

There are concerns that the use of CLA by overweight people may tend to cause or to aggravate insulin resistance, which may increase their risk of developing diabetes.^[31][32] However, the evidence is controversial, and some studies showed no changes in insulin sensitivity.^[33][34]

In one study CLA produced a 32% increase in biliary cholesterol concentration which increases the chance of gallstone formation.^[35]

In 2006, a study by the US Department of Agriculture suggested that CLA can induce essential fatty acid redistribution in mice. Changes in docosahexaenoic acid (DHA) and arachidonic acid (AA) levels were observed in some organs. For instance, certain CLA isomers reduced the DHA content of heart tissue by 25%, while in the spleen, DHA content rose, and AA fell.^[4] A study of CLA supplementation in hatchling chicks (2005) showed high mortality and low hatchability rates among CLA-supplemented groups, and also a decrease in brain DHA levels of CLA-treated chicks[1]. These studies raise the question of whether CLA may increase the risk of cardiovascular and inflammatory diseases, but it has yet to be established whether such changes occur in humans, and whether they are clinically relevant.

[edit] Dietary Sources

Of all foods, kangaroo meat may have the highest concentration of CLA.^[36] Food products (e.g. mutton and beef) from grass-fed ruminants are good sources of CLA, and contain much more of it than those from grain-fed animals.^[37] In fact, meat and dairy products from grass-fed animals can produce 300-500% more CLA than those of cattle fed the usual diet of 50% hay and silage, and 50% grain.^[38]

Eggs are also rich in CLA, and it has been shown that CLA in eggs survives the temperatures encountered during frying.^[39]

Some mushrooms like Agaricus bisporus, are a rare vegetable source of CLA.^[40]

[edit] See also

• Conjugated fatty acids

[edit] References