Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references
Conjugated linoleic acid (CLA) refers to a family of many isomers of linoleic acid (at least 13 are reported), which are found primarily in the meat and dairy products of ruminants. As implied by the name, the double bonds of CLAs are conjugated.
CLA were first isolated by Pariza in 1983 from ground meat but their structure was determined later.
Most studies of CLA have used a mixture of isomers wherein the c9, t11-CLA and t10, c12-CLA isomers were the most abundant.
Conjugated linoleic acid is a trans fat, though some researchers claim that it is not harmful in the same fashion as other trans fatty acids, but rather is beneficial. CLA is a conjugated system, and in the United States, trans linkages in a conjugated system are not counted as trans fat for the purposes of nutritional regulations and labeling. CLA, as well as some trans isomers of oleic acid, is produced by microorganisms in the rumen of ruminants. Non-ruminants, such as humans, are able to produce some isomers of CLA from some trans isomers of oleic acid, such as vaccenic acid, which is converted to CLA by delta-9-desaturase.
Diet and health
Various antioxidant and anti-tumor properties have been attributed to CLA, and studies on mice and rats show promising results in reducing mammary, skin, and colon tumor growth ; however, it is suspected that sufficient concentrations to achieve anti-inflammatory effects within human tissues may not be attainable via oral consumption.
A European team lead by the Swiss scientist Lukas Rist has found that mothers consuming mostly organic milk and meat products have about 50 percent higher levels of rumenic acid in their breast milk. 
Studies on CLA in humans shows a tendency for reduced body fat particularly abdominal fat, changes in serum total lipids and decreased whole body glucose uptake. The maximum reduction in body fat mass was achieved with a 3.4 g daily dose. CLA supplementation has, however, been shown to increase C-reactive protein levels and to induce oxidative stress and to reduce insulin sensitivity and increase lipid peroxidation.
Possible side effects of CLA in humans
There are concerns that the use of CLA by overweight people may actually cause insulin resistance, leading to an increased risk for developing diabetes.
A recent study (2006) conducted in mice by the US Department of Agriculture gives account of some highly concerning effects of CLA: it can dramatically induce essential fatty acid redistribution (DHA and AA) in various organ tissues.
The same study raises the concern that it might pose significant risks, especially regarding cardiovascular health and inflammatory diseases. DHA content in heart tissue for instance was found to be reduced by no less than 25% by certain CLA isomers, while spleen DHA increased 6-fold and spleen AA was reduced to only 5% of its normal levels in that tissue.
. Another study (2005) of CLA supplementation of hatching chicks showed high mortality and low hatchability rate among the CLA-supplemented groups, and also a decrease in brain DHA levels of CLA-incubated chicks. 
Kangaroo meat may have the highest concentration of CLA when compared with other foods.
Food products of grass-fed ruminants (e.g. lamb, beef) are good sources, and contain much more CLA than those from grain-fed animals. 
In fact, products of grass fed animals can produce 300-500% more CLA than cows fed the typical diet of 50% hay and silage, with 50% grain.
Eggs are also rich in CLA, and it has been shown that the CLA in eggs survives the high temperatures encountered during frying.
Conjugated fatty acids
^ Ha YL, Grimm NK, Pariza MW (1987). "Anticarcinogens from fried ground beef: heat-altered derivatives of linoleic acid". Carcinogenesis8 (12): 1881–7. PMID 3119246.
^ ab Fatty Acid Profiles of Liver, Adipose Tissue, Speen, and Heart of Mice Fed Diets Containing T10, C-12-, and C9, T11-Conjugated Linoleic Adic.
^ 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. PMID 16571155.
^ 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 Cancer41 (1-2): 91-7. PMID 12094634.
^ Belury, M.A. (Oct 2002). "Inhibition of carcinogenesis by conjugated linoleic acid: Potential mechanisms of action". Journal of Nutrition132 (10): 2995–2998. PMID 12368384. Retrieved on 2007-08-23.
^ Lukas Rist, Andre Mueller, Christiane Barthel, Bianca Snijders, Margje Jansen, A. Paula Simoes-Wust, Machteld Huber, Ischa Kummeling, Ursula von Mandach, Hans Steinhart, and Carel Thijs. (June 2007). "Influence of organic diet on the amount of conjugated linoleic acids in breast milk". British Journal of Nutrition.
^ Thom E, Wadstein J, Gudmundsen O. (Sep-Oct 2001). "Conjugated linoleic acid reduces body fat in healthy exercising humans.". The Journal of International Medical Research29 (5): 392-396. PMID 11725826. Retrieved on 2006-05-27.
^ Blankson H, Stakkestad JA, Fagertun H, Thom E, Wadstein J, Gudmundsen O. (December 2000). "Conjugated linoleic acid reduces body fat mass in overweight and obese humans.". Journal of Nutrition130 (12): 2943-2948. PMID 11110851. Retrieved on 2006-05-27.
^ Risérus U, Basu S, Jovinge S, Fredrikson GN, Arnlöv J, Vessby B (2002). "Supplementation with conjugated linoleic acid causes isomer-dependent oxidative stress and elevated C-reactive protein: a potential link to fatty acid-induced insulin resistance". Circulation106 (15): 1925-9. PMID 12370214.
^ Risérus U, Smedman A, Basu S, Vessby B (2003). "CLA and body weight regulation in humans". Lipids38 (2): 133-7. PMID 12733745.
^ 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. 01.CIR.0000033589.15413.48v1. Retrieved on 2007-02-19.
^ A natural quick fix - What Doctors Don't Tell You 2. HealthWorld Online,. Retrieved on 2007-11-05.
^ Commonwealth Scientific and Industrial Research Organisation (CSIRO) (2004-04-23). "Kangaroo meat - health secret revealed". Press release. Retrieved on 2007-01-23.
^ T. R. Dhiman, L. D. Satter, M. W. Pariza, M. P. Galli, K. Albright, and M. X. Tolosa (May 2000). "Conjugated Linoleic Acid (CLA) Content of Milk from Cows Offered Diets Rich in Linoleic and Linolenic Acid". Journal of Dairy Science83 (5): 1016-1027. PMID 10821577. Retrieved on 2006-05-27.
^ T. R. Dhiman (2001). "Role of diet on conjugated linoleic acid content of milk and meat.". Journal of Animal Science79. Retrieved on 2007-03-09.
^ Lin Yang, Ying Cao, Zhen-Yu Chen (2004). "Stability of conjugated linoleic acid isomers in egg yolk lipids
during frying". Food Chemistry86: 531–535. Elsevier. doi:10.1016/j.foodchem.2003.09.006.
Al Sarakbi W, Salhab M, Mokbel K. Dairy products and breast cancer risk: a review of the literature. Int J Fertil Women's Med. 2005 Nov-Dec;50(6):244-9. Review.
Bhattacharya A, Banu J, Rahman M, Causey J, Fernandes G. Biological effects of conjugated linoleic acids in health and disease. J Nutr Biochem. 2006 Dec;17(12):789-810. Epub 2006 May 2. Review.
Ip MM, Masso-Welch PA, Ip C. Prevention of mammary cancer with conjugated linoleic acid: role of the stroma and the epithelium. J Mammary Gland Biol Neoplasia. 2003 Jan;8(1):103-18. Review.
Kritchevsky D. Antimutagenic and some other effects of conjugated linoleic acid // British Journal of Nutrition. – 2000. – 83, N 5. – P. 459-465.
Larsson S. C., Bergkvist L., Wolk A. High-fat dairy food and conjugated linoleic acid intakes in relation to colorectal cancer incidence in the Swedish Mammography Cohort // American Journal of Clinical Nutrition. – 2005. – 82, N 4. – P. 894-900.
Lee KW, Lee HJ, Cho HY, Kim YJ. Role of the conjugated linoleic acid in the prevention of cancer. Crit Rev Food Sci Nutr. 2005;45(2):135-44. Review.
Maynard L. J., Franklin S. T. Functional foods as a value-added strategy: the commercial potential of "cancer-fighting" dairy products // Review of Agricultural Economics. – 2003. – 25, N 2. – P. 316-331.
Miller Á., Stanton C., Murphy J., Devery R. Conjugated linoleic acid (CLA)-enriched milk fat inhibits growth and modulates CLA-responsive biomarkers in MCF-7 and SW480 human cancer cell lines // British Journal of Nutrition. – 2003. – 90, N 5. – P. 877-885.
Pariza MW, Park Y, Cook ME. Conjugated linoleic acid and the control of cancer and obesity. Toxicol Sci. 1999 Dec;52 (2 Suppl):107-10. Review.
Tanaka K. Occurrence of conjugated linoleic acid in ruminant products and its physiological functions // Animal Science Journal. – 2005. – 76, N 4. – P. 291-303.
Voorrips L. E., Brants H. A. M., Kardinaal A. F. M., Hiddink G. J., Brandt P. A., van den Goldbohm R. A. Intake of conjugated linoleic acid, fat, and other fatty acids in relation to postmenopausal breast cancer: the Netherlands cohort study on diet and cancer // American Journal of Clinical Nutrition. – 2002. – 76, N 4. – P. 873-882.