Conjugated linoleic acid
Conjugated linoleic acids (CLA) are a family of at least 28 isomers of linoleic acid found mostly in the meat and dairy products derived from ruminants. CLAs can be either cis- or trans-fats and the double bonds of CLAs are conjugated and separated by a single bond between them.
CLA is marketed under the name Tonalin as a dietary supplement on the basis of its supposed health benefits. There is, however, no convincing evidence that taking CLA supplements has any benefits for human health.
The biological activity of CLA was noted by researchers in 1979 who found it to inhibit chemically induced cancer in mice. In 2004, one of those researchers noted that the scientific literature was "growing at a phenomenal rate".
The United States Food and Drug Administration categorizes CLA as generally recognized as safe (GRAS) status for certain food categories, including fluid milk, yogurt, meal replacement shakes, nutritional bars, fruit juices and soy milk. With GRAS status, food companies are able to add CLA to products in these food categories.
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. More recent studies using individual isomers indicate that the two isomers have very different health effects.
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. 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.
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 and/or dysbiosis.
CLA is marketed in dietary supplement form for its supposed anti-cancer benefit (for which there is no evidence) and as a bodybuilding aid. A 2004 review of the evidence said that while CLA seemed to benefit animals, there was a lack of good evidence of human health benefits, despite the many claims made for it.
CLA has no useful benefit for overweight or obese people as it has no long-term effect on body composition.
CLA has shown an effect on insulin response in diabetic rats but there is no evidence of this effect in humans.
Kangaroo meat may have the highest concentration of CLA. 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. In fact, meat and dairy products from grass-fed animals can produce 300-500% more CLA than those of cattle fed the usual diet of 50% hay and silage, and 50% grain.
- Banni S (June 2002). "Conjugated linoleic acid metabolism". Current Opinion in Lipidology 13 (3): 261–6. doi:10.1097/00041433-200206000-00005. PMID 12045395.
- Talbott SM, Hughes K (2007). "Conjugated linoleic acid". The Health Professional's Guide to Dietary Supplements. The Health Professional's Guide to Dietary Supplements (Lippincott Williams & Wilkins). pp. 14–. ISBN 978-0-7817-4672-4.
- Rainer L, Heiss CJ; Heiss (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.
- Onakpoya IJ, Posadzki PP, Watson LK, Davies LA, Ernst E; Posadzki; Watson; Davies; Ernst (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.
- Ha YL, Grimm NK, Pariza MW; Grimm; Pariza (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.
- Pariza MW (June 2004). "Perspective on the safety and effectiveness of conjugated linoleic acid". Am. J. Clin. Nutr. 79 (6 Suppl): 1132S–1136S. PMID 15159246.
- "Fatty Acid Profiles of Liver, Adipose Tissue, Speen, and Heart of Mice Fed Diets Containing T10, C-12-, and C9, T11-Conjugated Linoleic Adic".
- 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. PMID 15321800.
- Ulf Risérus, MMed; Samar Basu, PhD; Stefan Jovinge, MD, PhD; Gunilla Nordin Fredrikson, PhD; Johan Ärnlöv, MD; Bengt Vessby, MD, PhD (September 2002). "Supplementation With Conjugated Linoleic Acid Causes Isomer-Dependent Oxidative Stress and Elevated C-Reactive Protein". American Heart Association Journals 106 (15): 1925–9. doi:10.1161/01.CIR.0000033589.15413.48. PMID 12370214. 01.CIR.0000033589.15413.48v1. Retrieved 2007-02-19.
- II International Congress on CLA from Experimental Models to Human Application
- Kuhnt K, Kraft J, Moeckel P, Jahreis G; Kraft; Moeckel; Jahreis (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.
- Banni S, Angioni E, Murru E, Carta G, Melis M, Bauman D, Dong Y, Ip C; Angioni; Murru; Carta; Melis; Bauman; Dong; Ip (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:10.1207/S15327914NC41-1&2_12 (inactive 2015-01-11). PMID 12094634.
- Carina Paola Van Nieuwenhove, Victoria Terán and Silvia Nelina González. "Chapter 3: Conjugated Linoleic and Linolenic Acid Production by Bacteria: Development of Functional Foods". In Everlon Cid Rigobelo. Probiotics. doi:10.5772/50321.
- Estelle Devillard, Freda M. McIntosh, Sylvia H. Duncan, and R. John Wallace (March 2007). "Metabolism of Linoleic Acid by Human Gut Bacteria: Different Routes for Biosynthesis of Conjugated Linoleic Acid". Journal of Bacterioly 189 (6): 2566–2570. doi:10.1128/JB.01359-06.
- E. Barrett, R. P. Ross, G. F. Fitzgerald, and C. Stanton1 (April 2007). "Rapid Screening Method for Analyzing the Conjugated Linoleic Acid Production Capabilities of Bacterial Cultures". Applied and Environmental Microbioly 73 (7): 2333–2337. doi:10.1128/AEM.01855-06. PMC 1855641. PMID 17277221.
- Gorissen L, De Vuyst L, Raes K, De Smet S, Leroy F.; De Vuyst; Raes; De Smet; Leroy (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.
- Esther Jiméneza, M. Antonia Villar-Tajadurab, María Marína, Javier Fontechab, Teresa Requenac, Rebeca Arroyoa, Leónides Fernándeza and Juan M. Rodrígueza (July 2012). "Complete Genome Sequence of Bifidobacterium breve CECT 7263, a Strain Isolated from Human Milk". Journal of Bacterioly 194 (14): 3762–3763. doi:10.1128/JB.00691-12. PMC 3393482. PMID 22740680.
- Davì G, Santilli F, Patrono C; Santilli; Patrono (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.
- "Kangaroo meat - health secret revealed" (Press release). Commonwealth Scientific and Industrial Research Organisation (CSIRO). 2004-04-23. Retrieved 2007-01-23.
- T. R. Dhiman, L. D. Satter, M. W. Pariza, M. P. Galli, K. Albright, and 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.
- T. R. Dhiman (2001). "Role of diet on conjugated linoleic acid content of milk and meat" (PDF). Journal of Animal Science 79. Retrieved 2007-03-09.
- Lin Yang, Ying Cao, Zhen-Yu Chen; Cao; 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.
- 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.
- 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.