What are Omega-3 fatty acids?
The three types of omega-3 fatty acids involved in human physiology are α-linolenic acid (ALA) (found in plant oils), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) (both commonly found in marine oils). Marine algae and phytoplankton are primary sources of omega-3 fatty acids.
Fatty acids are named by the location of the first double bond, counted from the methyl end, that is, the omega (ω-) or the n- end. Omega 3 fatty acids are polyunsaturated fatty acids (PUFAs) with a double bond (C=C) at the 'third carbon atom' from the end of the carbon chain. There are 11 different types of Omega-3 fatty acids. The three most important ones are EPA, DHA and ALA.
EPA Omega-3 fatty acid--In chemical structure, EPA is a carboxylic acid with a 20-carbon chain and five cis double bonds; the first double bond is located at the third carbon from the omega end.
DHA Omega-3 fatty acid-- is a carboxylic acid with a 22-carbon chain and six cis double bonds with the first double bond located at the third carbon from the omega end. DHA is one of the more important of the Omega-3's: the majority of the omega-3 fatty acids in both the brain (97%) and the retina (93%) are made of DHA. DHA is a key component in the heart, has anti-inflammatory properties.
ALA Omega-3 fatty acid-- is an essential fatty acid (along with linolenic acid) that cannot be produced by the body and must be aquired through diet. ALA (α-Linolenic acid) is a carboxylic acid with an 18-carbon chain and three cis double bonds. The first double bond is located at the third carbon from the methyl end of the fatty acid chain
Role of Omega-3 Fatty Acids in Health
Humans are unable to synthesize omega-3 fatty acids, but can obtain the shorter-chain omega-3 fatty acid ALA (18 carbons and 3 double bonds) through diet and use it to form the more important long-chain omega-3 fatty acids, EPA (20 carbons and 5 double bonds) and then from EPA, the most crucial, DHA (22 carbons and 6 double bonds). The ability to make the longer-chain omega-3 fatty acids from ALA may be impaired in aging.
Some research suggests that the anti-inflammatory activity of long-chain omega-3 fatty acids may translate into clinical effects. most notably, these include cardiovascular diseases, inflammatory bowel disease (IBD), cancer, and rheumatoid arthritis, but psychiatric and neurodegenerative illnesses are other examples. see Abstract
An omega-3 fatty acid known as docosahexaenoic acid, or DHA, seems to reverse the harmful changes produced by fructose. (See Review)
Notes on DHA -- DHA strengthens synapses in the brain and enhances learning and memory. It is abundant in wild salmon (but not in farmed salmon) and, to a lesser extent, in other fish and fish oil, as well as walnuts, flaxseed, and fruits and vegetables.
DHA is the most abundant omega-3 fatty acid in the brain and retina. DHA comprises 40% of the polyunsaturated fatty acids (PUFAs) in the brain and 60% of the PUFAs in the retina. Fifty percent of the weight of a neuron's plasma membrane is composed of DHA. DHA is richly supplied during breastfeeding, and DHA levels are high in breastmilk regardless of dietary choices.
DHA deficiency is associated with cognitive decline. (See Abstract).
What Foods have the most amounts of Omega-3 Fatty Acids?
For total omega-3 values-- Grams of omega-3 per 3oz serving: Flaxseed 11.3, Walnuts 3.0, Sardines and Herring 1.3-2.0, Salmon 1.1-1.9, Mackerel 1.1-1.9, Swordish 0.97.
Note: One-quarter cup of flaxseeds contains about 6.3 grams of omega-3 fatty acids while one-quarter cup of walnuts contains about 2.7 grams. In either case, the amount is pretty substantial. Therefore by combining one-quarter cup of walnuts with a tablespoon of flaxseeds you will add close to the recommended 4 grams of omega-3 fats to your diet. (See Reference 4)
Note on DHA--"DHA is mainly found in animal products such as fish, eggs and meats. Oily fish, such as mackerel, herring, salmon, trout, sardines, pilchards, are the richest dietary source of EFAs, containing 10 to 100 times more DHA than non-marine food sources such as nuts, seeds, wholegrains and dark green, leafy vegetables."
Readings and References
See also Fats in Cooking and Health
Science of Chocolate