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Conjugated linoleic acid

Group of compounds found in meat and dairy from ruminants

Group of compounds found in meat and dairy from ruminants

Conjugated linoleic acids (CLA) are a family of isomers of linoleic acid. In principle, 28 isomers are possible. CLA is found mostly in the meat and dairy products derived from ruminants. The two C=C double bonds are conjugated (i.e., separated by a single bond) as opposed by "typical" polyunsaturated fatty acids where double bonds are separated by two single bonds. CLAs are simultaneously both cis-fats and trans-fats, as one of the two C=C bonds is cis and the other trans.

CLA is naturally present in milkfat and beef, has shown some potentially beneficial effects on rodent models of cardiometabolic disease, and is also available as a dietary supplement.

Biochemistry

CLA describes a variety of isomers of octadecadienoic fatty acids.

Commonly, CLAs are studied as some mixture of isomers wherein the isomers c9,t11-CLA (rumenic acid) and t10,c12-CLA were the most abundant.{{cite web |url-status = live |archive-url = https://web.archive.org/web/20070301045910/http://www.ars.usda.gov/research/publications/publications.htm?seq_no_115=179685 |archive-date = 2007-03-01 |doi-access= free

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, or dysbiosis.

Health effects

CLA is marketed in dietary supplement form for its supposed anti-cancer benefit (for which there is a lack of robust evidence or well-accepted mechanism, and very few studies conducted so far) and as a bodybuilding aid. A 2004 review of the evidence said that while CLA seemed beneficial in animal models, there was a lack of good evidence for health benefits in humans despite the many claims made for CLA supplementation.

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

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. 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. Some mushrooms, such as Agaricus bisporus and Agaricus subrufescens, are rare non-animal sources of CLA.

However, dietary punicic acid—which is abundant in pomegranate seeds—is converted to the rumenic acid (which is 9Z11E-CLA) upon absorption in rats, suggesting that non-animal sources can still effectively provide dietary CLA.

History

In 1979 CLAs were found to inhibit chemically-induced cancer in mice and research on its biological activity has continued.

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

References

References

  1. (2004-04-01). "REVIEWS: Conjugated Linoleic Acid: Historical Context and Implications". The Professional Animal Scientist.
  2. Tricon S. (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..
  3. "II International Congress on CLA from Experimental Models to Human Application".
  4. (April 2006). "Trans-11-18 : 1 is effectively Delta9-desaturated compared with trans-12-18 : 1 in humans". Br J Nutr.
  5. (2001). "Vaccenic acid feeding increases tissue levels of conjugated linoleic acid and suppresses development of premalignant lesions in rat mammary gland". Nutr Cancer.
  6. (March 2007). "Metabolism of Linoleic Acid by Human Gut Bacteria: Different Routes for Biosynthesis of Conjugated Linoleic Acid". Journal of Bacteriology.
  7. E. Barrett. (April 2007). "Rapid Screening Method for Analyzing the Conjugated Linoleic Acid Production Capabilities of Bacterial Cultures". Applied and Environmental Microbiology.
  8. (April 2012). "Conjugated linoleic and linolenic acid production kinetics by bifidobacteria differ among strains". International Journal of Food Microbiology.
  9. (July 2012). "Complete Genome Sequence of Bifidobacterium breve CECT 7263, a Strain Isolated from Human Milk". Journal of Bacteriology.
  10. (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.
  11. (2007). "The Health Professional's Guide to Dietary Supplements". Lippincott Williams & Wilkins.
  12. (June 2004). "Conjugated linoleic acid: health implications and effects on body composition". J Am Diet Assoc.
  13. (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.
  14. (August 2010). "Nutraceuticals in diabetes and metabolic syndrome". Cardiovascular Therapeutics.
  15. (1 May 2000). "Conjugated Linoleic Acid (CLA) Content of Milk from Cows Offered Diets Rich in Linoleic and Linolenic Acid". Journal of Dairy Science.
  16. (2004). "Stability of conjugated linoleic acid isomers in egg yolk lipids during frying". Elsevier.
  17. (2006). "Anti-aromatase activity of phytochemicals in white button mushrooms (Agaricus bisporus)". Cancer Res..
  18. W. J. Jang S. W. Hyung. "Production of natural c9,t11 conjugated linoleic acid (c9,t11 CLA) by submerged liquid culture of mushrooms".
  19. (1 August 2006). "Conjugated linolenic acid is slowly absorbed in rat intestine, but quickly converted to conjugated linoleic acid". J Nutr.
  20. (1987). "Anticarcinogens from fried ground beef: heat-altered derivatives of linoleic acid". Carcinogenesis.
  21. Pariza MW. (June 2004). "Perspective on the safety and effectiveness of conjugated linoleic acid". Am. J. Clin. Nutr..
  22. (July 25, 2008). "CLA approved as food ingredient". University of Wisconsin Madison.
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