Omega-3 Fatty Acid

Omega-3 Fatty Acids (Omega-3s) are polyunsaturated fats with a double bond at the third carbon atom from the end of the carbon chain. As omega is the last letter in the Greek alphabet, the term "omega-3" denotes the double bond occurring three carbons from the end. They are also sometimes referred to as "n-3 fatty acids" in scientific literature.

Relationship of Omega-3s to Omega-6s

Within the human body, omega-3s and omega-6 fatty acids essentially "compete" with one another for a limited amount of enzymes available to desaturate and elongate them into the long chain highly unsaturated fatty acids the body needs. Therefore, the amount of omega-3s needed for optimal health depends on the amount of omega-6s consumed as well. One study sets the ideal ratio is 2.3:1, or 2.3g omega-6s for every 1g of omega-3s consumed. However, a more commonly cited optimal ratio is 4:1.

A study published in 2000 estimated that polyunsaturated fatty acids make up about 19-22% of fat intake in the diets of adult Americans. The vast majority (89%) of the polyunsaturated fat consumed is linoleic acid, an omega-6 fatty acid, compared to only 9%-11% from alpha-linoleic acid (ALA), an omega-3. The most common sources of ALA in the American diet are canola and soybean oils. During the study period, American adults consumed an estimated 1.1–1.6g of ALA per day. They consumed less than 0.2g/day of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) combined.

The study states:

"The ratio of 2.3:1 translates to 6.7g n-6 fatty acids and 2.9g n-3 fatty acids in a 8360 kJ (2000 kcal) diet. The difficulty in meeting the recommended ratio is that many foods typically consumed in the American diet simply have a ratio of n-6 to n-3 fatty acids far above 2.3:1. Even if fish consumption is increased to achieve the goal of 0.65 g/d of EPA and DHA, the ratio will not be markedly lowered unless n-6 fatty acid consumption is decreased markedly."

The study estimated per capita linoleic acid (omega-6) consumption at 11-16g/day. Therefore, reducing omega-6 consumption to 6.7g/day would mean cutting it roughly in half.

According to another source, author Susan Allport, reducing our omega-6:omega-3 ratio in our diets to 4:1 "produces a 1:1 ratio of HUFAs [highly unsaturated fatty acids] in cell membranes."

Types of Omega-3 Fatty Acids

Fats are categorized by the number of carbons in them, the number of double bonds, and the placement of the double bonds in their chemical structures. Omega-3s are notated as "n-3."

The following are all omega-3s:

• Alpha-Linolenic Acid (ALA) (18:3n-3)
• Stearidonic Acid (SDA) (18:4n-3)
• Eicosapentaenoic Acid (EPA) (20:5n−3)
• Docosapentaenoic Acid (DPA) (22:5n-3)
• Docosahexaenoic Acid (DHA) (22:6n−3)

The human body converts ALA to EPA and DHA using a series of elongation and desaturation processes. It elongates the chain by adding additional carbons, and it desaturates it (of hydrogen) by adding more double-bonds between carbons (in place of what was previously bonds with hydrogen molecules).

First, the body uses an enzyme called delta-6-desaturase to turn ALA (18:3n-3) into SDA (18:4n-3). Then it uses the enzyme elongase-5 to add two carbons, making 20:4n-3. Then it uses an enzyme called delta-5-desaturase to add another double-bond, creating EPA (20:5n-3).

The body can then elongate EPA using elongase-2 to form 22:5n-3 and then 24:5n-3. Using delta-6-desaturase, it can then add one more double-bond to create 24:6n-3. Then it can undergo one round of beta-oxidation to form DHA (22:6n-3).

These same enzymes are used in a parallel process converting the omega-6 fatty acid linoleic acid (LA) (18:2n-6) to longer chain, highly unsaturated fatty acids. Delta-6-desaturase first converts LA to gamma-linolenic acid (GLA) (18:3n-6). This is elongated by elongase to 20:3n-6 and then desaturated once again using delta-5-desaturase to arachidonic acid 20:4n-6. Further elongation creates 22:4n-6 and 24:4n-6 and then delta-6-desaturase desaturates it to 24:5n-6. Last, one round of beta-oxidation creates 22:5n-6.

Because the two families of polyunsaturated fats (omega 3 and omega 6) are competing for the use of the same enzymes, the consumption of one influences the metabolism of the other. If one consumes them at a ratio of 14:1 (omega-6/omega-3), the presence in the tissues will be equal. Thus, omega-3s are stronger at competing for the enzymes than omega-6s.

Sources of Omega-3 Fatty Acids

A 2013 study by Washington State University research Charles Benbrook (who is also on the Science Advisory Board of the Organic Center) and others found that "organic milk contained 25% less ω-6 fatty acids and 62% more ω-3 fatty acids than conventional milk, yielding a 2.5-fold higher ω-6/ω-3 ratio in conventional compared to organic milk (5.77 vs. 2.28)" and that "dairy products supply far more α-linolenic acid than seafoods, about one-third as much eicosapentaenoic acid, and slightly more docosapentaenoic acid, but negligible docosahexaenoic acid."

Articles and Resources

Related SourceWatch articles

• Omega-6 Fatty Acid
• Polyunsaturated Fat
• Alpha Linolenic Acid (ALA)
• Eicosapentaenoic Acid (EPA)
• Docosahexaenoic Acid (DHA)

Related PRWatch Articles

• Jill Richardson, Is Monsanto's New Genetically Engineered Soy a Health Food?, PRWatch, May 16, 2013.
• Rebekah Wilce, Spinning Suspect Ingredients in Baby Formula, PRWatch, February 22, 2012.

External Resources

• Charles Benbrook, Gillian Butler, Maged A. Latif, Carlo Leifert, and Donald R. Davis, Organic Production Enhances Milk Nutritional Quality by Shifting Fatty Acid Composition: A United States–Wide, 18-Month Study, PLoS ONE 8(12): e82429, December 9, 2013.
• Susan Allport, The Queen of Fats: Why Omega-3s Were Removed From the Western Diet and What We Can Do To Replace Them, University of California Press, Los Angeles, 2006.

External Articles

• Sarah K. Abbott, Paul L. Else, Taleitha A. Atkins, A.J. Hulbert, "Fatty acid composition of membrane bilayers: Importance of diet polyunsaturated fat balance," Biochimica et Biophysica Acta (BBA) - Biomembranes, Volume 1818, Issue 5, May 2012, Pages 1309–1317.
• Robert A. Gibson, Bev Muhlhausler, Maria Makrides, "Conversion of linoleic acid and alpha-linolenic acid to long-chain polyunsaturated fatty acids (LCPUFAs), with a focus on pregnancy, lactation and the first 2 years of life," Maternal & Child Nutrition, March 2, 2011.
• Gwendolyn Barceló-Coblijn, Eric J. Murphy, "Alpha-linolenic acid and its conversion to longer chain n−3 fatty acids: Benefits for human health and a role in maintaining tissue n−3 fatty acid levels," Progress in Lipid Research, Volume 48, Issue 6, November 2009, Pages 355–374.
• Brenna JT, Salem N Jr, Sinclair AJ, Cunnane SC, "alpha-Linolenic acid supplementation and conversion to n-3 long-chain polyunsaturated fatty acids in humans," Prostaglandins, Leukotrienes, and Essential Fatty Acids, 2009, 80(2-3):85-91.
• Lands B, "A critique of paradoxes in current advice on dietary lipids," Prog Lipid Res. 2008 Mar;47(2):77-106. doi: 10.1016/j.plipres.2007.12.001. Epub 2007 Dec 15.
• Rapoport SI, Rao JS, Igarashi M. "Brain metabolism of nutritionally essential polyunsaturated fatty acids depends on both the diet and the liver," Prostaglandins Leukotrienes and Essential Fatty Acids, 2007;77:251–61.
• Nahed Hussein, Eric Ah-Sing, Paul Wilkinson, Clare Leach, Bruce A. Griffin, and D. Joe Millward, "Long-chain conversion of 13Clinoleic acid and alpha-linolenic acid in response to marked changes in their dietary intake in men," Journal of Lipid Research, 2005, 46, 269-280.
• Graham C. Burdge and Philip C. Calder, "α-Linolenic acid metabolism in adult humans: the effects of gender and age on conversion to longer-chain polyunsaturated fatty acids," European Journal of Lipid Science and Technology, Volume 107, Issue 6, pages 426–439, No. 6 June 2005.
• James MJ, Ursin VM, Cleland LG, "Metabolism of stearidonic acid in human subjects: comparison with the metabolism of other n-3 fatty acids," American Journal of Clinical Nutrition, 2003 May;77(5):1140-5.
• Cunnane SC, "Problems with essential fatty acids: time for a new paradigm?," Prog Lipid Res 2003;42:544–68.
• Sinclair AJ, Attar-Bashi NM, Li D, "What is the role of alpha-linolenic acid for mammals?" Lipids, 2002;37:1113–23.
• Lauritzen L, Hansen HS, Jorgensen MH, Michaelsen KF, "The essentiality of long chain n-3 fatty acids in relation to development and function of the brain and retina," Progress in Lipid Research, 2001;40:1–94.
• PM Kris-Etherton, Denise Shaffer Taylor, Shaomei Yu-Poth, Peter Huth, Kristin Moriarty, Valerie Fishell, Rebecca L Hargrove, Guixiang Zhao, and Terry D Etherton, "Polyunsaturated fatty acids in the food chain in the United States," American Journal of Clinical Nutrition, 2000;71(suppl):179S–88S.
• Holman RT. "The slow discovery of the importance of omega 3 essential fatty acids in human health," J Nutr 1998;128:427S–33S.
• Lands WE, Morris A, Libelt B, "Quantitative effects of dietary polyunsaturated fats on the composition of fatty acids in rat tissues," Lipids, 1990.
• Artemis Simopoulos, Salem N Jr. n-3 Fatty acids in eggs from range-fed Greek chickens. New England Journal of Medicine, 1989;321:1412–5.
• Holman RT. "Biological activities of and requirements for polyunsaturated fatty acids," Prog Chem Fats Other Lipids 1968;9:611–80.
• Mohrhauer H, Christiansen K, Gan MV, Deubig M, Holman RT. "Chain elongation of linoleic acid and its inhibition by other fatty acids in vitro," Journal of Biological Chemistry, 1967;242:4507–14.
• Brenner RR, Peluffo RO, "Effect of saturated and unsaturated fatty acids on the desaturation in vitro of palmitic, stearic, oleic, linoleic, and linolenic acids," Journal of Biological Chemistry, 1966;241:5213–9.