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Omega-6 fatty acid

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The chemical structure of linoleic acid, a common omega-6 fatty acid found in many nuts, seeds and vegetable oils.

Omega-6 fatty acids (also referred to as ω-6 fatty acids or n-6 fatty acids) are a family of polyunsaturated fatty acids[1] that have in common a final carbon-carbon double bond in the n-6 position, that is, the sixth bond, counting from the methyl end.[2]

The biological effects of the omega-6 fatty acids are largely mediated by their conversion to omega-6 eicosanoids that bind to diverse receptors found in every tissue of the body. The conversion of tissue arachidonic acid (20:4n-6) to omega-6 prostaglandin and omega-6 leukotriene hormones provides many targets for pharmaceutical drug development and treatment to diminish excessive omega-6 actions in atherosclerosis,[3] asthma, arthritis, vascular disease, thrombosis, immune-inflammatory processes, and tumor proliferation. Competitive interactions with the omega-3 fatty acids affect the relative storage, mobilization, conversion and action of the omega-3 and omega-6 eicosanoid precursors (see Essential fatty acid interactions).

Key omega−6 fatty acids

Linoleic acid (18:2, n−6), the shortest-chained omega−6 fatty acid, is an essential fatty acid. Arachidonic acid (20:4) is a physiologically significant omega−6 fatty acid and is the precursor for prostaglandins, endocannabinoids and other physiologically active molecules.

Suggested negative health effects

Some medical research suggests that excessive levels of certain omega−6 fatty acids relative to certain omega-3 fatty acids may increase the probability of a number of diseases.[4][5][6] However, scientific research indicates that air pollution, smoking, second-hand smoke, and other exogenous toxins cause the initial inflammation in the cells which leads to the overexpression of the COX-2 enzyme and subsequently to the overproduction of inflammatory promoting prostaglandins from Arachidonic acid for the purpose of alerting the immune system of the cell damage and eventually to the production of anti-inflammatory prostaglandins during the resolution phase of inflammation, after the cell damage has been repaired.[7][8][9][10][11]

Modern Western diets typically have ratios of omega−6 to omega−3 in excess of 10 to 1, some as high as 30 to 1; the average ratio of omega-6 to omega-3 in the Western diet is 15/1–16.7/1.[3] Humans are thought to have evolved with a diet of a 1-to-1 ratio of omega-6 to omega-3 and the optimal ratio is thought to be 4 to 1 or lower,[3][12] and it is even better if there is more omega−3 than omega−6 (especially healthy ratio of omega−6 to omega−3 is from 1:1 to 1:4).[13] A ratio of 2–3/1 omega 6 to omega 3 helped reduce inflammation in patients with rheumatoid arthritis.[3] A ratio of 5/1 had a beneficial effect on patients with asthma but a 10/1 ratio had a negative effect.[3] A ratio of 2.5/1 reduced rectal cell proliferation in patients with colorectal cancer, whereas a ratio of 4/1 had no effect.[3]

Excess omega−6 fatty acids from vegetable oils interfere with the health benefits of omega−3 fats, in part because they compete for the same rate-limiting enzymes. A high proportion of omega−6 to omega−3 fat in the diet shifts the physiological state in the tissues toward the pathogenesis of many diseases: prothrombotic, proinflammatory and proconstrictive.[14]

Chronic excessive production of omega−6 eicosanoids is correlated with arthritis, inflammation, and cancer. Many of the medications used to treat and manage these conditions work by blocking the effects of the COX-2 enzyme.[15] Many steps in formation and action of omega-6 prostaglandins from omega-6 arachidonic acid proceed more vigorously than the corresponding competitive steps in formation and action of omega-3 hormones from omega-3 eicosapentaenoic acid.[16] The COX-1 and COX-2 inhibitor medications, used to treat inflammation and pain, work by preventing the COX enzymes from turning arachidonic acid into inflammatory compounds.[17] (See Cyclooxygenase for more information.) The LOX inhibitor medications often used to treat asthma, work by preventing the LOX enzyme from converting arachidonic acid into the leukotrienes.[18][19] Many of the anti-mania medications used to treat bipolar disorder work by targeting the arachidonic acid cascade in the brain.[20]

A high consumption of oxidized polyunsaturated fatty acids (PUFAs), which are found in most types of vegetable oil, may increase the likelihood that postmenopausal women will develop breast cancer.[21] Similar effect was observed on prostate cancer, but the study was performed on mice.[22] Another "analysis suggested an inverse association between total polyunsaturated fatty acids and breast cancer risk, but individual polyunsaturated fatty acids behaved differently [from each other]. [...] a 20:2 derivative of linoleic acid [...] was inversely associated with the risk of breast cancer".[23]

List of omega−6 fatty acids

Common name Lipid name Chemical name
Linoleic acid (LA) 18:2 (n−6) all-cis-9,12-octadecadienoic acid
Gamma-linolenic acid (GLA) 18:3 (n−6) all-cis-6,9,12-octadecatrienoic acid
Calendic acid 18:3 (n−6) 8E,10E,12Z-octadecatrienoic acid
Eicosadienoic acid 20:2 (n−6) all-cis-11,14-eicosadienoic acid
Dihomo-gamma-linolenic acid (DGLA) 20:3 (n−6) all-cis-8,11,14-eicosatrienoic acid
Arachidonic acid (AA) 20:4 (n−6) all-cis-5,8,11,14-eicosatetraenoic acid
Docosadienoic acid 22:2 (n−6) all-cis-13,16-docosadienoic acid
Adrenic acid 22:4 (n−6) all-cis-7,10,13,16-docosatetraenoic acid
Docosapentaenoic acid 22:5 (n−6) all-cis-4,7,10,13,16-docosapentaenoic acid
Tetracosatetraenoic acid 24:4 (n−6) all-cis-9,12,15,18-tetracosatetraenoic acid
Tetracosapentaenoic acid 24:5 (n−6) all-cis-6,9,12,15,18-tetracosapentaenoic acid

Dietary linoleic acid requirement

Adding more controversy to the omega−6 fat issue is that the dietary requirement for linoleic acid has been questioned, because of a significant methodology error proposed by University of Toronto scientist Stephen Cunnane.[24] Cunnane proposed that the seminal research used to determine the dietary requirement for linoleic acid was based on feeding animals linoleic acid-deficient diets, which were simultaneously deficient in omega−3 fats. The omega−3 deficiency was not taken into account. The omega−6 oils added back systematically to correct the deficiency also contained trace amounts of omega−3 fats. Therefore the researchers were inadvertently correcting the omega−3 deficiency as well. Ultimately, it took more oil to correct both deficiencies. According to Cunnane, this error overestimates linoleic acid requirements by 5 to 15 times.

Dietary sources

File:Oenothera biennis 20050825 962.jpg
The evening primrose flower (O. biennis) produces an oil containing a high content of γ-linolenic acid, a type of omega−6 fatty acid.

Four major food oils (palm, soybeans, rapeseed, and sunflower) provide more than 100 million metric tons annually, providing more than 32 million metric tons of omega-6 linoleic acid and 4 million metric tons of omega-3 alpha-linolenic acid.[25]

Dietary sources of omega−6 fatty acids include:[26]

See also

Notes and references

  1. Omega-3 Fatty Acids, Hepatic Lipid Metabolism, and Nonalcoholic Fatty Liver Disease Annual Review of Nutrition Vol. 33: 231-248 (Volume publication date July 2013) DOI: 10.1146/annurev-nutr-071812-161230
  2. Chow, Ching Kuang (2001). Fatty Acids in Foods and Their Health Implications. New York: Routledge Publishing. OCLC 25508943. Template:Pn
  3. 3.0 3.1 3.2 3.3 3.4 3.5 Simopoulos, A.P (2002). "The importance of the ratio of omega-6/omega-3 essential fatty acids". Biomedicine & Pharmacotherapy 56 (8): 365–79. doi:10.1016/S0753-3322(02)00253-6. PMID 12442909. 
  4. Lands, W. E.M. (2005). "Dietary Fat and Health: The Evidence and the Politics of Prevention: Careful Use of Dietary Fats Can Improve Life and Prevent Disease". Annals of the New York Academy of Sciences 1055: 179–92. doi:10.1196/annals.1323.028. PMID 16387724. 
  5. Hibbeln, Joseph R; Nieminen, Levi RG; Blasbalg, Tanya L; Riggs, Jessica A; Lands, William EM (2006). "Healthy intakes of n−3 and n−6 fatty acids: estimations considering worldwide diversity". The American Journal of Clinical Nutrition 83 (6 Suppl): 1483S–1493S. PMID 16841858. 
  6. Okuyama, H.; Ichikawa, Y.; Sun, Y.; Hamazaki, T.; Lands, W.E.M. (2006). "ω3 Fatty Acids Effectively Prevent Coronary Heart Disease and Other Late-Onset Diseases – The Excessive Linoleic Acid Syndrome". in Okuyama, H.. Prevention of Coronary Heart Disease. World Review of Nutrition and Dietetics. pp. 83–103. doi:10.1159/000097809. ISBN 3-8055-8179-3. 
  7. Zhao, Yutong; Usatyuk, Peter V.; Gorshkova, Irina A.; He, Donghong; Wang, Ting; Moreno-Vinasco, Liliana; Geyh, Alison S.; Breysse, Patrick N. et al. (2009). "Regulation of COX-2 Expression and IL-6 Release by Particulate Matter in Airway Epithelial Cells". American Journal of Respiratory Cell and Molecular Biology 40 (1): 19–30. doi:10.1165/rcmb.2008-0105OC. PMID 18617679. 
  8. Calderón-Garcidueñas, Lilian; Reed, William; Maronpot, Robert; Henriquez-Roldán, Carlos; Delgado-Chavez, Ricardo; Carlos Henriquez-Roldán, Ana; Dragustinovis, Irma; Franco-Lira, Maricela et al. (2004). "Brain Inflammation and Alzheimer's-Like Pathology in Individuals Exposed to Severe Air Pollution". Toxicologic Pathology 32 (6): 650–8. doi:10.1080/01926230490520232. PMID 15513908. 
  9. Moraitis, Dimitrios; Du, Baoheng; De Lorenzo, Mariana S.; Boyle, Jay O.; Weksler, Babette B.; Cohen, Erik G.; Carew, John F.; Altorki, Nasser K. et al. (2005). "Levels of Cyclooxygenase-2 Are Increased in the Oral Mucosa of Smokers: Evidence for the Role of Epidermal Growth Factor Receptor and Its Ligands". Cancer Research 65 (2): 664–70. PMID 15695412. 
  10. Yang, Chuen-Mao; Lee, I-Ta; Lin, Chih-Chung; Yang, Ya-Lin; Luo, Shue-Fen; Kou, Yu Ru; Hsiao, Li-Der (2009). "Cigarette smoke extract induces COX-2 expression via a PKCα/c-Src/EGFR, PDGFR/PI3K/Akt/NF-κB pathway and p300 in tracheal smooth muscle cells". American Journal of Physiology - Lung Cellular and Molecular Physiology 297 (5): L892–902. doi:10.1152/ajplung.00151.2009. PMID 19717552. 
  11. Martey, Christine A.; Stephen J., Pollock; Chantal K., Turner; Katherine M. A., O'Reilly; Carolyn J., Baglole; Richard P., Phipps; Patricia J., Sime (2004). "Cigarette smoke induces cyclooxygenase-2 and microsomal prostaglandin E2 synthase in human lung fibroblasts: Implications for lung inflammation and cancer". American Journal of Physiology - Lung Cellular and Molecular Physiology 287 (5): L981–91. doi:10.1152/ajplung.00239.2003. PMID 15234907. 
  12. Daley, C. A.; Abbott, A.; Doyle, P.; Nader, G.; and Larson, S. (2004). A literature review of the value-added nutrients found in grass-fed beef products. California State University, Chico (College of Agriculture). Retrieved 2008-03-23. 
  13. Lands, WEM (2005). Fish, Omega 3 and human health. American Oil Chemists' Society. ISBN 978-1-893997-81-3. Template:Pn
  14. Simopoulos, A.P. (2003). "Importance of the Ratio of Omega-6/Omega-3 Essential Fatty Acids: Evolutionary Aspects". in Simopoulos, Artemis P.; Cleland, Leslie G.. Omega-6/Omega-3 Essential Fatty Acid Ratio: The Scientific Evidence. World Review of Nutrition and Dietetics. 92. pp. 1–22. doi:10.1159/000073788. ISBN 3-8055-7640-4. 
  15. Smith, William L. (2008). "Nutritionally essential fatty acids and biologically indispensable cyclooxygenases". Trends in Biochemical Sciences 33 (1): 27–37. doi:10.1016/j.tibs.2007.09.013. PMID 18155912. 
  16. Wada, M.; Delong, C. J.; Hong, Y. H.; Rieke, C. J.; Song, I.; Sidhu, R. S.; Yuan, C.; Warnock, M. et al. (2007). "Enzymes and Receptors of Prostaglandin Pathways with Arachidonic Acid-derived Versus Eicosapentaenoic Acid-derived Substrates and Products". Journal of Biological Chemistry 282 (31): 22254–66. doi:10.1074/jbc.M703169200. PMID 17519235. 
  17. Cleland, Leslie G; James, Michael J; Proudman, Susanna M (2006). "Fish oil: what the prescriber needs to know". Arthritis Research & Therapy 8 (1): 202. doi:10.1186/ar1876. PMID 16542466. 
  18. Mickleborough, Timothy (2005). "Dietary Omega-3 Polyunsaturated Fatty Acid Supplementation and Airway Hyperresponsiveness in Asthma". Journal of Asthma 42 (5): 305–14. doi:10.1081/JAS-200062950. PMID 16036405. 
  19. K S Broughton; Johnson, CS; Pace, BK; Liebman, M; Kleppinger, KM (1997-04-01). "Reduced asthma symptoms with n-3 fatty acid ingestion are related to 5-series leukotriene production". The American Journal of Clinical Nutrition 65 (4): 1011–7. PMID 9094887. 
  20. Lee, Ho-Joo; Rao, Jagadeesh S.; Rapoport, Stanley I.; Bazinet, Richard P. (2007). "Antimanic therapies target brain arachidonic acid signaling: Lessons learned about the regulation of brain fatty acid metabolism". Prostaglandins, Leukotrienes and Essential Fatty Acids 77 (5–6): 239–46. doi:10.1016/j.plefa.2007.10.018. PMID 18042366. 
  21. Sonestedt, Emily; Ericson, Ulrika; Gullberg, Bo; Skog, Kerstin; Olsson, Håkan; Wirfält, Elisabet (2008). "Do both heterocyclic amines and omega-6 polyunsaturated fatty acids contribute to the incidence of breast cancer in postmenopausal women of the Malmö diet and cancer cohort?". International Journal of Cancer 123 (7): 1637–43. doi:10.1002/ijc.23394. PMID 18636564. 
  22. Yong Q. Chen, at al (2007). "Modulation of prostate cancer genetic risk by omega-3 and omega-6 fatty acids". The Journal of Clinical Investigation 117 (7): 1866–1875. doi:10.1172/JCI31494. PMID 17607361. 
  23. Pala, Valeria; Krogh, Vittorio; Muti, Paola; Chajès, Véronique; Riboli, Elio; Micheli, Andrea; Saadatian, Mitra; Sieri, Sabina et al. (2001). "Erythrocyte Membrane Fatty Acids and Subsequent Breast Cancer: A Prospective Italian Study". Journal of the National Cancer Institute 93 (14): 1088–95. doi:10.1093/jnci/93.14.1088. PMID 11459870. 
  24. Cunnane, Stephen C. (2003). "Problems with essential fatty acids: Time for a new paradigm?". Progress in Lipid Research 42 (6): 544–68. doi:10.1016/S0163-7827(03)00038-9. PMID 14559071. 
  25. Gunstone, Frank (December 2007). "Market update: Palm oil". International News on Fats, Oils and Related Materials 18 (12): 835–6. 
  26. "Food sources of total omega 6 fatty acids". Retrieved 2011-09-04. 
  27. Kids veggie food, omega 6 sources Various sources referenced including pine nuts, pecans and walnuts
  28. Nutrition Facts about coconut

Additional sources

External links

  • Erasmus, Udo (1993). Fats That Heal, Fats That Kill (3rd ed.). Burnaby (BC): Alive Books. ISBN 978-0-920470-38-1.