The long and short of omega-3 fatty acids
ALA (alpha-linoleic acid) (C18:3n-3) is a short-chain essential omega-3 fatty acid; flaxseed oil is a good source of ALA.
EPA (eicosapentaenoic acid; 20 carbons) and DHA (decosahexaenoic acid; 22 carbons) are long-chain essential omega-3 fatty acids; fish oil is a good source of EPA and DHA.
ALA → EPA → DHA
EPA can be synthesized in the body from ALA, but DHA must be made from EPA (whether from dietary EPA or synthesized from ALA).1 DHA is therefore more likely to be deficient in the body if not included in the diet.
Further, the evidence for a beneficial effect of long-chain omega-3 fatty acids (EPA and DHA) is greater than that for the short-chain ALA.2
The omega-6:omega-3 ratio
Although omega-6 (n-6) fatty acids are prevalent in the diet, omega-3 (n-3) fatty acids are relatively uncommon. Many Americans do not reach the recommended daily intake of omega-3. Clients should pay attention to the composition of PUFA, not just the total PUFA content, and look for products high in omega-3.
The optimal ratio of omega-6:omega-3 is thought to be approximately 5–8:1, with some countries recommending an even lower ratio.1,3,4 The ratio in the US diet, however, is approximately 10–15:1.1,4
A lower ratio of omega-6:omega-3 has been associated with a reduction in chronic disease risk.1 It has been suggested by AHA that it is better to raise this ratio by increasing omega-3 than by reducing omega-6 because this may have a negative impact on heart health.5 This is because omega-6 and omega-3 compete for the same enzymes that make long-chain fatty acids, which in turn are precursors for proinflammatory prostaglandins, leukotrienes, and thromboxanes.1 The metabolites of omega-6 fatty acids are more inflammatory than those of omega-3.1
References: 1. Simopoulos AP. The importance of the omega-6/omega-3 fatty acid ratio in cardiovascular disease and other chronic diseases. Exp Biol Med. 2008;233:674–688. 2. Van Horn L, McCoin M, Kris-Etherton PM, et al. The evidence for dietary prevention and treatment of cardiovascular disease. J Am Diet Assoc. 2008;108:287–331. 3. Position of the American Dietetic Association and the Dietitians of Canada. Dietary fatty acids. J Am Diet Assoc. 2007;107:1599–1611. 4. Kris-Etherton PM, Taylor DS, Yu-Poth S, et al. Polyunsaturated fatty acids in the food chain in the United States. Am J Clin Nutr. 2000;71(suppl):179S–188S. 5. Harris WS, Mozaffarian D, Rimm E, et al. Omega-6 fatty acids and risk for cardiovascular disease: a science advisory from the American Heart Association Nutrition Subcommittee of the Council on Nutrition, Physical Activity, and Metabolism; Council on Cardiovascular Nursing; and Council on Epidemiology and Prevention. Circulation. 2009;119:902–907.