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What is it?
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 programme 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):
| Rating | Health Concerns |
|---|---|
 |
Athletic performance (body composition and strength) |
Reliable and relatively consistent scientific data showing a substantial health benefit. Contradictory, insufficient, or preliminary
studies suggesting a health benefit or minimal health benefit. For an herb, supported by traditional use but
minimal or no scientific evidence. For a supplement, little scientific support and/or minimal
health benefit. | |
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?
Overweight volunteers who took 4.5 grams of CLA per day for one year had an increase in their blood levels of lipoprotein(a), a risk factor for heart disease.16 While the significance of this change is not certain, it is possible that long-term use of CLA could increase the risk of developing heart disease.
In a double-blind study of people with type 2 diabetes, supplementing with 3 grams of CLA per day for eight weeks significantly increased blood glucose levels by 6.3% and decreased insulin sensitivity.17 A reduction in insulin sensitivity was also seen in a study of overweight men without diabetes after treatment with 3 grams of CLA per day for three months,18 although in a study of young sedentary men, 4 grams of CLA per day for eight weeks improved insulin sensitivity.19 Thus, although the studies are conflicting, CLA may be harmful for some people who have, or are at risk of developing, diabetes. One unpublished human trial reported isolated cases of gastrointestinal upset.20
At the time of writing, there were no well-known drug interactions with conjugated linoleic acid.
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. Gaullier JM, Halse J, Hoye K, et al. Conjugated linoleic acid supplementation for 1 y reduces body fat mass in healthy overweight humans. Am J Clin Nutr 2004;79:1118–25.
17. Moloney F, Yeow TP, Mullen A, et al. Conjugated linoleic acid supplementation, insulin sensitivity, and lipoprotein metabolism in patients with type 2 diabetes mellitus. Am J Clin Nutr 2004;80:887-95.
18. Riserus U, Vessby B, Arnlov J, Basu S. Effects of cis-9,trans-11 conjugated linoleic acid supplementation on insulin sensitivity, lipid peroxidation, and proinflammatory markers in obese men. Am J Clin Nutr 2004;80:279–83.
19. Eyjolfson V, Spriet LL, Dyck DJ. Conjugated linoleic acid improves insulin sensitivity in young, sedentary humans. Med Sci Sports Exerc 2004;36:814–20.
20. 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].
