Linoleic acid metabolism

Conjugated linoleic acid

Conjugated linoleic acids (CLA) are a family of at least 13 isomers of linoleic acid found especially in the meat and dairy products derived from ruminants. As the name implies, the double bonds of CLAs are conjugated.

History

CLAs were first isolated in 1983, by M. W. Pariza, from ground meat. Their structure was determined later.

Biochemistry

Most studies of CLAs have used a mixture of isomers wherein the isomers c9, t11-CLA and t10, c12-CLA were the most abundant ones.

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 is not harmful, but beneficial. 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.

Diet and health

Antioxidant and anti-cancer properties have been attributed to CLA, and studies on mice and rats show encouraging results in hindering the growth of tumors in mammary, skin, and colon tissues.

A European team led 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 of CLA in human diets show that it tends to reduce body fat, particularly abdominal fat, improves serum lipid profiles, and decreases whole-body glucose uptake. The maximum reduction in body fat was achieved with a daily dose of 3.4g. CLA supplementation has, however, been shown to increase C-reactive protein levels, possibly to induce oxidative stress, to reduce insulin sensitivity, and to increase lipid peroxidation. However, the significance of these findings is unknown, and other studies suggest that CLA may protect cells from oxidative damage by increasing glutathione levels without inducing lipid peroxidation. It is possible, however, that the observation of markers of increased lipid oxidation may indicate potentially desirable lipolytic effects. Further studies are necessary to establish the clinical significance of such observations.

Possible side effects of CLA in humans

There are concerns that the use of CLA by overweight people may tend to cause or to aggravate insulin resistance, which may increase their risk of developing diabetes. However, the evidence is controversial, and some studies showed no changes in insulin sensitivity.

In one study CLA produced a 32% increase in biliary cholesterol concentration which increases the chance of gallstone formation.

In 2006, a study by the US Department of Agriculture suggested that CLA can induce essential fatty acid redistribution in mice. Changes in docosahexaenoic acid (DHA) and arachidonic acid (AA) levels were observed in some organs. For instance, certain CLA isomers reduced the DHA content of heart tissue by 25%, while in the spleen, DHA content rose, and AA fell. A study of CLA supplementation in hatchling chicks (2005) showed high mortality and low hatchability rates among CLA-supplemented groups, and also a decrease in brain DHA levels of CLA-treated chicks These studies raise the question of whether CLA may increase the risk of cardiovascular and inflammatory diseases, but it has yet to be established whether such changes occur in humans, and whether they are clinically relevant.

Dietary Sources

Of all foods, kangaroo meat may have the highest concentration of CLA. Food products (e.g. mutton and beef) from grass-fed ruminants 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.

Eggs are also rich in CLA, and it has been shown that CLA in eggs survives the temperatures encountered during frying.

See also

References

General references

  • 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.
  • Belury M. A. Dietary conjugated linoleic acid in health: physiological effects and mechanisms of action // Annu. Rev. Nutr. – 2002. – 22. – P. 505–531.
  • Bauman D. E., Corl B. A., Baumgard L. H., Griinari J. M. Conjugated linoleic acid (CLA) and the dairy cow // In Recent Advances in Animal Nutrition / Ed. P. C. Garnsworthy, J. Wiseman; Nottingham Univ. Press. – Nottingham, UK, 2001 – P. 221–250.
  • Schmid A., Collomb M., Sieber R., Bee G. Conjugated linoleic acid in meat and meat products: A review // Meat Science. – 2006. – 73. – P. 29–41.
  • Harefoot C. G., Hazlewood G. P. Lipid metabolism in the rumen / In: Hobson P. N., Stewart C. S. (Eds.), The Rumen Microbial Ecosystem, second ed. Blackie Academic, London, 1999. – P. 382–426.
  • Jenkins T. C., McGuire M. A. Major advances in nutrition: impact on milk composition // J. Dairy Sci. – 2006. – 89 (4) – Р. 1302–1310.

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