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> Nutritional and Dietary Supplements > Conjugated Linoleic Acid
CONJUGATED LINOLEIC ACIDVisit The Healthy Living Bookshelf:
What does it do? Conjugated linoleic acid (CLA) is a slightly altered form of the essential fatty acid linoleic acid. Preliminary animal and test tube research suggests that CLA might reduce the risk of cancers at several sites, including breast, prostate, colorectal, lung, skin, and stomach.1 2 3 4 Whether CLA will have a similar protective effect for people has yet to be demonstrated in human research. In a double-blind study, volunteers participating in an exercise program received 600 mg of CLA or a placebo three times per day for 12 weeks. Compared with placebo, CLA significantly reduced percent body fat, but did not significantly reduce body weight.5 In a double-blind study of obese men, supplementation with 4.2 grams of CLA per day for four weeks produced a small but statistically significant reduction in waist size. However, compared with the placebo, CLA did not promote weight loss.6 At present, there is not sufficient evidence to support the use of CLA as a treatment for obesity. Animal research suggests an effect of CLA supplementation on reducing body fat.7 8 Limited controlled human research found 5.6–7.2 grams per day of CLA produced nonsignificant gains in muscle size and strength in experienced9 and inexperienced10 weight-training men. Animal research also suggests an effect of CLA supplementation on limiting food allergy reactions,11 preventing atherosclerosis,12 13 and improving glucose tolerance.14 As with the cancer research, the effects of CLA on these conditions in humans remains unclear. Where is it found? CLA is found mainly in dairy products and also in beef and poultry, eggs, and corn oil. Bacteria that live in the intestine of humans can produce CLA from linoleic acid, but supplementation of a rich source of linoleic acid did not produce increases in blood levels of CLA in one human study.15 CLA is available as a supplement.  CLA has been used in connection with the following conditions (refer to the individual health concern for complete information):
Who is likely to be deficient? No deficiencies of CLA are reported or believed to occur, since it is not an essential nutrient. How much is usually taken? Animal research uses very large amounts, equivalent to several grams per day for humans. Until human research is conducted with CLA, the appropriate amount to take of this nutrient remains unclear. Are there any side effects or interactions? The side effects of CLA are unknown, due to the limited research in humans. However, one unpublished human trial reported isolated cases of gastrointestinal upset.16 References: 
1. Cesano A, Visonneau S, Scimeca JA, et al. Opposite effects of linoleic acid and conjugated linoleic acid on human prostatic cancer in SCID mice. Anticancer Res 1998;18:1429–34. 2. Thompson H, Zhu Z, Banni S, et al. Morphological and biochemical status of the mammary gland as influenced by conjugated linoleic acid: implication for a reduction in mammary cancer risk. Cancer Res 1997;57:5067–72. 3. Ip C. Review of the effects of trans fatty acids, oleic acid, n-3 polyunsaturated fatty acids, and conjugated linoleic acid on mammary carcinogenesis in animals. Am J Clin Nutr 1997;66(suppl):1523S–29S [review]. 4. Parodi PW. Cows’ milk fat components as potential anticarcinogenic agents. J Nutr 1997;127:1055–60 [review]. 5. Thom E, Wadstein J, Gudmundsen O. Conjugated linoleic acid reduces body fat in healthy exercising humans. J Int Med Res 2001;29:392–6. 6. Riserus U, Berglund L, Vessby B. Conjugated linoleic acid (CLA) reduced abdominal adipose tissue in obese middle-aged men with signs of the metabolic syndrome: a randomised controlled trial. Int J Obes 2001;25:1129–35. 7. West DB, Delany JP, Camet PM, et al. Effects of conjugated linoleic acid on body fat and energy metabolism in the mouse. Am J Physiol 1998;275:R667–72. 8. Park Y, Albright KJ, Liu W, et al. Effect of conjugated linoleic acid on body composition in mice. Lipids 1997;32:853–8. 9. Ferreira M, Krieder R, Wilson M. Effects of CLA supplementation during resistance training on body composition and strength. J Strength Conditioning Res 1998;11:280. 10. Lowery LM, Appicelli PA, Lemon PWR. Conjugated linoleic acid enhances muscle size and strength gains in novice bodybuilders. Med Sci Sports Exerc 1998;30:S182 [abstract] 11. Sugano M, Tsujita A, Yamasaki M, et al. Conjugated linoleic acid modulates tissue levels of chemical mediators and immunoglobulins in rats. Lipids 1998;33:521–7. 12. Nicolosi RJ, Rogers EJ, Kritchevsky D, et al. Dietary conjugated linoleic acid reduces plasma lipoproteins and early aortic atherosclerosis in hypercholesterolemic hamsters. Artery 1997;22:266–77. 13. Lee KN, Kritchevsky D, Pariza MW, et al. Conjugated linoleic acid and atherosclerosis in rabbits. Atherosclerosis 1994;108:19–25. 14. Houseknecht KL, Vanden Heuvel JP, Moya-Camarena SY, et al. Dietary conjugated linoleic acid normalizes impaired glucose tolerance in the Zucker diabetic fatty fa/fa rat. Biochem Biophys Res Commun 1998;244:678–82. 15. Herbel BK, McGuire MK, McGuire MA, et al. Safflower oil consumption does not increase plasma conjugated linoleic acid concentrations in humans. Am J Clin Nutr 1998;67:332–7. 16. Thom E. A pilot study with the aim of studying the efficacy and tolerability of Tonalin CLA on the body composition in humans. Lillestrom, Norway: Medstat Research Ltd., July 1997 [unpublished]. |
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Reliable
and relatively consistent scientific data showing a substantial health benefit.
Contradictory, insufficient, or preliminary studies
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