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Conjugated Linoleic Acid (CLA):

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Aids in Controlling Weight, Heart Health and Mutagenic Concerns

By Kim Pryor and Jim English

Conjugated linoleic acid (CLA) is a naturally-occurring polyunsaturated fatty acid composed of positional and geometric isomers of linoleic acid (Fig. 1). The human body is unable to manufacture CLA, so it must be obtained from dietary sources. Since CLA is produced by microorganisms found in cows and other ruminant animals, foods highest in CLA include dairy products and meat, such as beef, lamb, and veal. Recently, CLA has become a popular supplement with bodybuilders due to its ability to promote muscle growth while reducing body fat.

Recently researchers have begun to uncover a host of unexpected health benefits of this unique dietary fat, including improved immune response, inhibition of cancer initiation, lowering of cholesterol levels, reduction of factors implicated in heart disease, and normalization of impaired glucose tolerance in diabetics.
CLA and Heart Disease
Researchers have found that conjugated linoleic acid acts as a powerful lipid-lowering and cardioprotective agent. In one study, researchers investigated the cholesterol-lowering effects of CLA on fifty hamsters fed either .06%, 11% or 1.1% concentrations of conjugated linoleic acid. Compared to controls, the CLA-treated animals collectively experienced a significant reduction in levels of plasma total cholesterol, LDL cholesterol, and triglycerides. The HDL cholesterol did not change, but resulted in a favorable change in the Cholesterol/HDL ratios. Interestingly, atherosclerosis took much longer to develop in the aortas of the CLA-treated groups than in the controls. (1)
In a second study, researchers at the University of Wisconsin-Madison fed 12 rabbits a diet containing 14% fat and 0.1% cholesterol for 22 weeks. For six of these rabbits, the diet was augmented with CLA (0.5 g CLA/rabbit per day). After 12 weeks, the researchers found that total and LDL cholesterol and triglycerides were markedly lower in the CLA-fed group. Interestingly, the LDL cholesterol-to-HDL cholesterol ratio and total cholesterol to HDL cholesterol ratio were significantly reduced in CLA-fed
rabbits. Examination of the aortas of CLA-fed rabbits showed less atherosclerosis than in controls. (2) Conjugated linoleic acid has also been found to prevent human platelet aggregation, significant in light of the role sticky cells play in strokes. (3)
Anti-Cancer Effects on Breast Cancer
In vivo animal studies and in vitro human cell cultures indicate that CLA may protect against prostate, mammary and colon cancer. A group of Cornell researchers conducted one particularly impressive study in which they induced experimental mammary cancer in rats. They then fed the animals either high CLA butter fat or a free fatty acid mixture of CLA isomers (typical of that found in supplemental CLA) during the time of pubescent mammary gland development.
Only 53% of the animals given CLA, both in the form of butter and free fatty acids, developed mammary tumors compared to 93% of controls! The researchers concluded that this laboratory animal model suggests that CLA could be beneficial in reducing the risk of breast cancer. According to Dale Bauman, one of the lead authors of the Cornell study, Most dietary substances exhibiting anti-carcinogenic activity are of plant origin and are only present at trace levels. However, CLA is found almost exclusively in animal products and is among the most potent of all naturally-occurring anti-carcinogens. (4)
Protects Against Colon and Prostate Cancer
Colon cancer is a leading cause of cancer-related deaths. One of the earliest changes in the colons of animals treated with carcinogens (such as the heterocyclic amines found in cooked meat) is the appearance of aberrant crypt focus (ACF), a biomarker for colon cancer. (5) Conjugated linoleic acid has been shown to inhibit ACF in rats. Furthermore, CLA may have an equally promising effect on prostate cancer. In one study using immunodeficient mice, researchers fed the animals either a standard diet
or diets supplemented with 1% linoleic acid or 1% conjugated linoleic acid. The researchers then inoculated the mice with human prostate cancer cells and continued to treat the animals with the two fatty acids. Mice fed the CLA-supplemented diet displayed not only smaller tumors than the other groups, but also a significant reduction in lung metastases, indicating that CLA was inhibiting the spread of the cancer. (6) In another study of animals with experimental breast cancer, this same inhibition of the spread of tumors occurred in proportion with increasing concentrations of dietary CLA. Conjugated linoleic acid was nearly as effective as indomethacin, a pharmaceutical suppressor of tumor growth and metastasis. (7)
Weight Loss and Muscle Building
Conjugated linoleic acid may have an equally important role to play in the areas of weight loss, body composition and muscle building. In animals, CLA has been shown to decrease body fat content by inhibiting fat storage and reducing the amount of fat deposited in the body. In one study, CLA-treated hamsters fed a high-fat, high cholesterol diet had significantly lower weight gain but greater food intake than controls. (8)
In another study, researchers found that pigs fed CLA showed a reduction in fat deposits of 31%, and an increase in lean tissue formation of 25% over an eight-week period. (9) Researchers theorized that dietary CLA repartitioned the delivery of fats, to enhance the transport of fats and other nutrients into muscle tissues, while promoting increased protein synthesis and lean muscle growth. (10)
CLA and Diabetes
Because CLA is functionally similar to certain insulin sensitizers, researchers were interested in its effects on diabetic rats. They discovered that this fatty acid normalized impaired glucose tolerance and alleviated hyperinsulinemia in the animals. (11) The researchers concluded that CLAs ability to improve glucose tolerance and restore glucose balance indicate that dietary conjugated linoleic acid may prove to be an important therapy for the prevention and treatment of diabetes.
Getting Lean with CLA
While many Americans have cut back on their consumption of beef and milk products, they have unwittingly increased their propensity to gain weight by lowering their intake of CLA from dietary sources. And since CLA is found in milk fats, drinking skim milk further deprives consumers of the health benefits of this unique and natural compound.
Studies suggest that taking 3 grams of CLA per day can reverse this problem and improve the muscle-to-fat ratio. By contributing to a loss of body fat, particularly abdominal fat, while increasing lean tissue formation, the result can be a leaner, and thus, healthier body.
References:
1. Nicolosi, RJ, Rogers EJ, Kritchevsky D, Scimeca JA, Huth PJ. Dietary conjugated inoleic acid reduces plasma lipoproteins and early aortic atharosclerosis in hypercholasterolemic hamsters. Artery (USA) , 1997,22/5 (266-277)
2. Lee K.N.; Kritchevsky D.; Pariza M.W. Conjugated linoleic acid and atherosclerosis in rabbits. Atherosclerosis (Ireland), 1994, 108/1 (19-25)
3. Truitt A, McNeill G, Vanderhoek JY. Antiplatelet effects of conjugated linoleic acid isomers. Biochim Biophys Acta 1999 May 18;1438(2):239-46.
4. Ip C, Banni S, Angioni E, Carta G, McGinley J, Thompson HJ, Barbano D, Bauman D. Conjugated Linoleic Acid-Enriched Butter Fat Alters Mammary Gland Morpogenesis and Reduces Cancer Risk in Rats. Journal of Nutrition, 129:2135-2142.
5. Dashwood, RH. Early detection and prevention of colorectal cancer (review). Oncol Rep 1999 Mar-Apr;6(2):277-81.
6. Cesano A. Visonneau S, Scimeca JA, Kritchevsky D, Santoli D. Opposite effects of linoleic acid and conjugated linoleic acid on human prostatic cancer in SCID mice. Anticancer Res 1998 May-Jun;18(3A):1429-34.
7. Hubbard NE, Lim D, Summers L, Erickson KL. Reduction of murine mammary tumor metastasis by conjugated linoleic acid. Cancer Lett 2000 Mar 13;150(1):93-100.
8. Gavino VC, Gavino G, Leblanc MJ, Tuchweber B. An isomeric mixture of conjugated linoleic acids but not pur cis-9, trans-11-octadecadienoic acid affects body weight gain and plasma lipids in hamsters. J Nutr 2000 Jan;130(1):27-9.
9. Ostrowska E, Muralitharan M, Cross RF, Bauman DE, Dunshea FR. Dietary conjugated linoleic acids increase lean tissue and decrease fat deposition in growing pigs. J Nutr 1999 Nov;129(11):2037-42.
10. Pariza MW, Park Y, Cook ME. Mechanisms of action of conjugated linoleic acid: evidence and speculation. Proc Soc Exp Biol Med 2000 Jan;223(1):8-13.
11. Houseknecht KL, Vanden Heuval JP, Moya-Camarena SY, Portocarrero CP, Peck LW, Nickel KP, Ebelury MA. Dietary conjugated linoleic acid normalizes impaired glucose tolerance in the Zucker diaetic fatty fa/fa rat. Biochem Biophys Res Commun 1998 Mar 27;244(3):678-82.

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