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The effects of conjugated linoleic acid on human health-related outcomes. Tricon S, Burdge GC, Williams CM, Calder PC, Yaqoob P. Proc Nutr Soc. 2005 May;64(2):171-82. Review. PMID: 15960862 Conjugated linoleic acid (CLA) is a collective term for a mixture of positional and geometric isomers of conjugated dienoic derivatives of linoleic acid. CLA has received considerable attention as a result of animal experiments that report anti-carcinogenic, anti-atherogenic and anti-diabetic properties, and modulation of body composition and immune function. Several studies of CLA supplementation in human subjects have now been published, but in contrast to animal studies there has been marked variation between reports on the health-related outcomes. The consensus from seventeen published studies in human subjects is that CLA does not affect body weight or body composition. Some detrimental effects of the trans-10,cis-12 CLA isomer have also been reported in terms of altered blood lipid composition and impaired insulin sensitivity. Finally, CLA has only limited effects on immune functions in man. However, there have been reports of some interesting isomer-specific effects of CLA on the blood lipid profile, but not on immune function. These isomer-specific effects need further investigation. Until more is known, CLA supplementation in man should be considered with caution.

Metabolic effects of conjugated linoleic acid in humans: the Swedish experience. Riserus U, Smedman A, Basu S, Vessby B. Am J Clin Nutr. 2004 Jun;79(6 Suppl):1146S-1148S. PMID: 15159248 CONCLUSIONS CLA and specifically the isolated isomers are interesting model fatty acids for studies of the effects of (structural differences of) unsaturated fatty acids in humans. Today, there is no clear indication for human use of CLA concentrates. The possible importance of the small reduction of body fat after supplementation with the commercially available CLA products, without evidence of an associated improvement in the metabolic profile, has to be weighed against the apparent reduction of HDL cholesterol and an increased lipid peroxidation. The possible health consequences of prolonged treatment periods are at present unknown. Human supplementation with high doses of the trans-10,cis-12 CLA isomer should be avoided while awaiting further information on possible effects and side effects. However, it cannot be excluded that future studies could point to clinical applications, eg, as a result of antitumorigenic properties or as a tool to prevent weight gain. This possibility certainly requires more research to increase the understanding of the mechanisms behind the effects of CLA and specific CLA isomers on a molecular level. More controlled studies in defined populations are needed, as are controlled studies for comparisons of the effects of different and well-defined (mixtures of) isomers and human studies of longer duration to secure long-term effects and safety.

Conjugated linoleic acid promotes human adipocyte insulin resistance through NFkappaB-dependent cytokine production. Chung S, Brown JM, Provo JN, Hopkins R, McIntosh MK. J Biol Chem. 2005 Nov 18;280(46):38445-56. Epub 2005 Sep 9. PMID: 16155293 doi: 10.1074/jbc.M508159200 Collectively, these data demonstrate for the first time that trans-10, cis-12 CLA promotes NFkappaB activation and subsequent induction of IL-6, which are at least in part responsible for trans-10, cis-12 CLA-mediated suppression of peroxisome proliferator-activated receptor gamma target gene expression and insulin sensitivity in mature human adipocytes. In summary, our in vitro data demonstrate that a physiological level of trans-10, cis-12 CLA activates NFκB- and ERK1/2-dependent cytokine production, which together suppress PPARγ and Glut4 levels and lead to impaired glucose uptake. Studies are currently under way examining 1) how CLA regulates PPARγ and the expression of its target genes, 2) the specific signaling role of SV cells and adipocytes in mediating the TG-lowering actions of CLA, and 3) the CLA-induced, upstream signal that activates NFκB and ERK1/2.

Opposing effects of cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acid on blood lipids in healthy humans. Tricon S, Burdge GC, Kew S, Banerjee T, Russell JJ, Jones EL, Grimble RF, Williams CM, Yaqoob P, Calder PC. Am J Clin Nutr. 2004 Sep;80(3):614-20. PMID: 15321800 Conclusion: Divergent effects of cis-9,trans-11 CLA and trans-10,cis-12 CLA appear on the blood lipid profile in healthy humans: trans-10,cis-12 CLA increases LDL:HDL cholesterol and total:HDL cholesterol, whereas cis-9,trans-11 CLA decreases them.

Consuming cheese from ewe's milk, rich in conjugated linoleic acid (CLA), may reduce markers linked to heart disease, suggest results from a small Italian study. Researchers from the University of Florence report that ewe's milk rich in cis-9, trans-11 CLA produced favourable changes in inflammatory cytokines and platelet aggregation, both of which are associated with atherosclerosis, or hardening of the arteries due to the build-up of fatty deposits on artery walls.

Effects of cis-9,trans-11 conjugated linoleic acid supplementation on insulin sensitivity, lipid peroxidation, and proinflammatory markers in obese men. Riserus U, Vessby B, Arnlov J, Basu S. Am J Clin Nutr. 2004 Aug;80(2):279-83. PMID: 15277146 CONCLUSIONS: A CLA preparation containing the purified c9,t11 CLA isomer increased insulin resistance and lipid peroxidation compared with placebo in obese men. Because c9,t11 CLA occurs in commercial supplements as well as in the diet, the present results should be confirmed in larger studies that also include women.

Conjugated linoleic acid impairs endothelial function. Taylor JS, Williams SR, Rhys R, James P, Frenneaux MP. Arterioscler Thromb Vasc Biol. 2006 Feb;26(2):307-12. Epub 2005 Dec 8. PMID: 16339498 CONCLUSIONS: A CLA isomeric mixture had at most modest effects on adiposity and worsened endothelial function. On the basis of these results, the use of the isomeric mixture of CLA as an aid to weight loss cannot be recommended

Conjugated linoleic acid improves insulin sensitivity in young, sedentary humans. Eyjolfson V, Spriet LL, Dyck DJ. Med Sci Sports Exerc. 2004 May;36(5):814-20. PMID: 15126715 CONCLUSIONS: Our results indicate that a common dosage of a commercially available CLA supplement can improve ISI in young, sedentary individuals. However, there is considerable individual variability in the response. Additional studies are required to identify underlying metabolic changes in human skeletal muscle.

Effects of dairy products naturally enriched with cis-9,trans-11 conjugated linoleic acid on the blood lipid profile in healthy middle-aged men. Tricon S, Burdge GC, Jones EL, Russell JJ, El-Khazen S, Moretti E, Hall WL, Gerry AB, Leake DS, Grimble RF, Williams CM, Calder PC, Yaqoob P. Am J Clin Nutr. 2006 Apr;83(4):744-53. PMID: 16600923 CONCLUSION: Dairy products naturally enriched with cis-9,trans-11 CLA and trans-11 18:1 do not appear to have a significant effect on the blood lipid profile

Conjugated linoleic acid supplementation for 1 y does not prevent weight or body fat regain. Larsen TM, Toubro S, Gudmundsen O, Astrup A. Am J Clin Nutr. 2006 Mar;83(3):606-12. PMID: 16522907 CONCLUSION: A 3.4-g daily CLA supplementation for 1 y does not prevent weight or fat mass regain in a healthy obese population.

White button mushroom (Agaricus bisporus) exhibits antiproliferative and proapoptotic properties and inhibits prostate tumor growth in athymic mice. Adams LS, Phung S, Wu X, Ki L, Chen S. Nutr Cancer. 2008;60(6):744-56. PMID: 19005974

Supplementation with trans10cis12-conjugated linoleic acid induces hyperproinsulinaemia in obese men: close association with impaired insulin sensitivity. Risérus U, Vessby B, Arner P, Zethelius B. Diabetologia. 2004 Jun;47(6):1016-9. Epub 2004 May 28. PMID: 15168020 DOI: 10.1007/s00125-004-1421-8 Conclusions/interpretation In obese men, t10c12CLA induces hyperproinsulinaemia that is related to impaired insulin sensitivity, independently of changes in insulin concentrations. These results are of clinical interest, as hyperproinsulinaemia predicts diabetes and cardiovascular disease. The use of weight-loss supplements containing this fatty acid is worrying.