Conjugated linoleic acid

Conjugated linoleic acids (CLA) are a family of at least 28[1] isomers of linoleic acid found mostly in the meat and dairy products derived from ruminants. Their two double bonds are conjugated (i.e., separated by a single bond). CLAs can be either cis-fats or trans-fats.

Rumenic acid, an example of conjugated linoleic acid

CLA is marketed as a dietary supplement on the basis of its supposed health benefits.[2]

History

The biological activity of CLA was noted by researchers in 1979 who found it to inhibit chemically-induced cancer in mice [3] and research on its biological activity has continued.[4]

In 2008, the United States Food and Drug Administration categorized CLA as generally recognized as safe (GRAS).[5]

Biochemistry

Most studies of CLAs have used a mixture of isomers wherein the isomers c9,t11-CLA (rumenic acid) and t10,c12-CLA were the most abundant.[6] More recent studies using individual isomers indicate that the two isomers have very different health effects.[7][8]

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 may have beneficial effects on human health.[9] 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.[10][11]

In healthy humans, CLA and the related conjugated linolenic acid (CLNA) isomers are bioconverted from linoleic acid and alpha-linolenic acid, respectively, mainly by Bifidobacterium bacteria strains inhabiting the gastrointestinal tract. However, this bioconversion may not occur at any significant level in those with a digestive disease, gluten sensitivity, or dysbiosis.[12][13][14][15]

Health

CLA is marketed in dietary supplement form for its supposed anti-cancer benefit (for which there is some evidence, but no known mechanism, and very few studies conducted so far)[16] and as a bodybuilding aid.[2] A 2004 review of the evidence said that while CLA seemed to benefit non-human animals, there was a lack of good evidence of human health benefits, despite the many claims made for it.[17]

Likewise, there is insufficient evidence that CLA has a useful benefit for overweight or obese people as it has no long-term effect on body composition.[18] Although CLA has shown an effect on insulin response in diabetic rats, there is no evidence of this effect in humans.[19]

A 2017 study found CLA supplementation has been associated with increased plasma C-reactive protein concentrations and a reduction in serum adiponectin concentrations, which indicates that CLA supplements have a pro-inflammatory effect.[20]

Dietary sources

Food products from grass-fed ruminants (e.g. mutton and beef) are good sources of CLA and contain much more of it than those from grain-fed animals.[21] Eggs from chickens that have been fed CLA are also rich in CLA, and CLA in egg yolks has been shown to survive the temperatures encountered during frying.[22] Some mushrooms, such as Agaricus bisporus and Agaricus subrufescens, are rare non-animal sources of CLA.[23][24] However, dietary punicic acid—which is abundant in pomegranate seeds—is converted to the CLA rumenic acid upon absorption in rats,[25] suggesting that non-animal sources can still effectively provide dietary CLA.

See also

References
  1. Banni S (June 2002). "Conjugated linoleic acid metabolism". Current Opinion in Lipidology. 13 (3): 261–6. doi:10.1097/00041433-200206000-00005. PMID 12045395. S2CID 30625824.
  2. Talbott SM, Hughes K (2007). "Conjugated linoleic acid". The Health Professional's Guide to Dietary Supplements. Lippincott Williams & Wilkins. pp. 14–. ISBN 978-0-7817-4672-4.
  3. Ha YL, Grimm NK, Pariza MW (1987). "Anticarcinogens from fried ground beef: heat-altered derivatives of linoleic acid". Carcinogenesis. 8 (12): 1881–7. doi:10.1093/carcin/8.12.1881. PMID 3119246.
  4. Pariza MW (June 2004). "Perspective on the safety and effectiveness of conjugated linoleic acid". Am. J. Clin. Nutr. 79 (6 Suppl): 1132S–1136S. doi:10.1093/ajcn/79.6.1132S. PMID 15159246.
  5. "CLA approved as food ingredient". University of Wisconsin Madison. July 25, 2008. Archived from the original on June 30, 2015. On July 24, the U.S. Food and Drug Administration announced its finding that conjugated linoleic acid, known as CLA, is "generally regarded as safe" for use in foods
  6. "Fatty Acid Profiles of Liver, Adipose Tissue, Speen, and Heart of Mice Fed Diets Containing T10, C-12-, and C9, T11-Conjugated Linoleic Adic". Archived from the original on 2007-03-01.
  7. Tricon S, Burdge GC, Kew S, et al. (September 2004). "Opposing effects of cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acid on blood lipids in most healthy humans". Am. J. Clin. Nutr. 80 (3): 614–20. doi:10.1093/ajcn/80.3.614. PMID 15321800.
  8. Ulf Risérus, MMed; Samar Basu; Stefan Jovinge, MD; Gunilla Nordin Fredrikson; Johan Ärnlöv, MD; Bengt Vessby, MD (September 2002). "Supplementation With Conjugated Linoleic Acid Causes Isomer-Dependent Oxidative Stress and Elevated C-Reactive Protein". Circulation. 106 (15): 1925–9. doi:10.1161/01.CIR.0000033589.15413.48. PMID 12370214. 01.CIR.0000033589.15413.48v1. Archived from the original on 2007-02-28. Retrieved 2007-02-19.
  9. milk.co.uk https://web.archive.org/web/20160808063946/http://www.milk.co.uk/page.aspx?intPageID=283. Archived from the original on 8 August 2016. Retrieved 23 April 2018. Missing or empty |title= (help)
  10. Kuhnt K, Kraft J, Moeckel P, Jahreis G (April 2006). "Trans-11-18 : 1 is effectively Delta9-desaturated compared with trans-12-18 : 1 in humans". Br J Nutr. 95 (4): 752–761. doi:10.1079/BJN20051680. PMID 16571155.
  11. Banni S, Angioni E, Murru E, Carta G, Melis M, Bauman D, Dong Y, Ip C (2001). "Vaccenic acid feeding increases tissue levels of conjugated linoleic acid and suppresses development of premalignant lesions in rat mammary gland". Nutr Cancer. 41 (1–2): 91–7. doi:10.1080/01635581.2001.9680617. PMID 12094634. S2CID 2920114.
  12. Estelle Devillard; Freda M. McIntosh; Sylvia H. Duncan; R. John Wallace (March 2007). "Metabolism of Linoleic Acid by Human Gut Bacteria: Different Routes for Biosynthesis of Conjugated Linoleic Acid". Journal of Bacteriology. 189 (6): 2566–2570. doi:10.1128/JB.01359-06. PMC 1899373. PMID 17209019.
  13. E. Barrett; R. P. Ross; G. F. Fitzgerald; and C. Stanton (April 2007). "Rapid Screening Method for Analyzing the Conjugated Linoleic Acid Production Capabilities of Bacterial Cultures". Applied and Environmental Microbiology. 73 (7): 2333–2337. doi:10.1128/AEM.01855-06. PMC 1855641. PMID 17277221.
  14. Gorissen L, De Vuyst L, Raes K, De Smet S, Leroy F (April 2012). "Conjugated linoleic and linolenic acid production kinetics by bifidobacteria differ among strains". International Journal of Food Microbiology. 155 (3): 234–240. doi:10.1016/j.ijfoodmicro.2012.02.012. PMID 22405353.
  15. Esther Jiméneza; M. Antonia Villar-Tajadurab; María Marína; Javier Fontechab; Teresa Requenac; Rebeca Arroyoa; Leónides Fernándeza; Juan M. Rodrígueza (July 2012). "Complete Genome Sequence of Bifidobacterium breve CECT 7263, a Strain Isolated from Human Milk" (PDF). Journal of Bacteriology. 194 (14): 3762–3763. doi:10.1128/JB.00691-12. PMC 3393482. PMID 22740680.
  16. Ochoa JJ, Farquharson AJ, Grant I, Moffat LE, Heys SD, Wahle KW (2004). "Conjugated linoleic acids (CLAs) decrease prostate cancer cell proliferation: different molecular mechanisms for cis-9, trans-11 and trans-10, cis-12 isomers". Carcinogenesis. 25 (7): 1185–91. doi:10.1093/carcin/bgh116. PMID 14976130.
  17. Rainer L, Heiss CJ (June 2004). "Conjugated linoleic acid: health implications and effects on body composition". J Am Diet Assoc (Review). 104 (6): 963–. doi:10.1016/j.jada.2004.03.016. PMID 15175596.
  18. Onakpoya IJ, Posadzki PP, Watson LK, Davies LA, Ernst E (March 2012). "The efficacy of long-term conjugated linoleic acid (CLA) supplementation on body composition in overweight and obese individuals: a systematic review and meta-analysis of randomized clinical trials". Eur J Nutr (Systematic review). 51 (2): 127–34. doi:10.1007/s00394-011-0253-9. PMID 21990002. S2CID 39625058.
  19. Davì G, Santilli F, Patrono C (August 2010). "Nutraceuticals in diabetes and metabolic syndrome". Cardiovasc Ther (Review). 28 (4): 216–26. doi:10.1111/j.1755-5922.2010.00179.x. PMID 20633024.
  20. "Review links conjugated linoleic acid supplementation to CRP". medicalxpress.com. Archived from the original on 26 March 2018. Retrieved 23 April 2018.
  21. T. R. Dhiman; L. D. Satter; M. W. Pariza; M. P. Galli; K. Albright; M. X. Tolosa (1 May 2000). "Conjugated Linoleic Acid (CLA) Content of Milk from Cows Offered Diets Rich in Linoleic and Linolenic Acid". Journal of Dairy Science. 83 (5): 1016–1027. doi:10.3168/jds.S0022-0302(00)74966-6. PMID 10821577. Retrieved 2006-05-27.
  22. Lin Yang; Ying Cao; Zhen-Yu Chen (2004). "Stability of conjugated linoleic acid isomers in egg yolk lipids during frying". Food Chemistry. Elsevier. 86 (4): 531–535. doi:10.1016/j.foodchem.2003.09.006.
  23. Chen, S.; Oh, SR; Phung, S; Hur, G; Ye, JJ; Kwok, SL; Shrode, GE; Belury, M; et al. (2006). "Anti-aromatase activity of phytochemicals in white button mushrooms (Agaricus bisporus)". Cancer Res. 66 (24): 12026–12034. doi:10.1158/0008-5472.CAN-06-2206. PMID 17178902.
  24. W. J. Jang S. W. Hyung. "Production of natural c9,t11 conjugated linoleic acid (c9,t11 CLA) by submerged liquid culture of mushrooms". Division of Applied Life Science (BK21), Graduate School, Gyeongsang National University, Jinju, 660-701, South Korea. Archived from the original on 2010-05-04. Cite journal requires |journal= (help)CS1 maint: location (link)
  25. Tsuzuki T, Kawakami Y, Abe R (1 August 2006). "Conjugated linolenic acid is slowly absorbed in rat intestine, but quickly converted to conjugated linoleic acid". J Nutr. 136 (8): 2153–9. doi:10.1093/jn/136.8.2153. PMID 16857834. Retrieved 2007-01-23.
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