GLOSSARY of LIPID TERMS

This glossary is of necessity a relatively short one. For a more detailed and comprehensive glossary of lipid terms, go to the website of the Oily Press at http://www.pjbarnes.co.uk/op/lg2pdf.htm  from which a downloadable  lipid glossary (extending to 245 pages) is available free of charge.

Alpha-linolenic Acid: ALA, 18:3n-3, 18:3w3 - Fatty acid with eighteen carbon atoms and three double bonds at carbons 9, 12 and 15, so that the last one is at the 3rd carbon from the terminal methyl end. It is a minor component of vegetable oils.

Arachidonic Acid (AA) 20:4n-6, 20:4w6 - A polyunsaturated fatty acid with a carbon chain of twenty carbon atoms and four double bonds at carbons 5, 8, 11 and 14, so that the last one is at the 6th carbon from the terminal methyl end. It is the most abundant polyunsaturated fatty acid in mammals, except in the brain and retina.

Diglyceride (Diacylglycerol) - Glycerol molecule with two of the three hydroxyl groups esterified by fatty acids.

Dihomogammalinolenic Acid (DGLA) – A polyunsaturated fatty acid with a carbon chain of twenty carbon atoms and three double bonds at carbons 8, 11 and 14, so that the last one is at the 6th carbon from the methyl end.

Docosahexaenoic Acid (DHA), 22:6n-3, 22:6w3 - One of the two major omega 3 polyunsaturated fatty acids found abundantly in fish oils, and the most abundant in the brain and retina. It has a carbon chain with twenty-two carbon atoms and six double bonds at carbons 4, 7, 10, 13, 16 and 19, so that the last one is at the 3rd carbon from the terminal methyl end.

Docosapentaenoic Acid (DPA) 22:5n-3, 22:5w3 (DPAn3) or 22:5n-3 22:5w6 (DPAn6) - A polyunsaturated fatty acid with a carbon chain of twenty-two carbon atoms and five double bonds at carbons 7, 10, 13, 16 and 19 (DPAn3) or carbons 4, 7, 10, 13 and 16 (DPAn6), so that the last one is at the 3rd (DPAn3) or the 6th (DPAn6) carbon from the terminal methyl end. DPAn6 is not normally found in human tissues, except when omega 3 deficiency occurs, when it is metabolised from AA as a substitute for DHA. DPAn3 is the third most abundant w-3 fatty acid in fish oil.

Double bond - Type of linkage between adjacent carbon atoms in a fatty acid, with two linkages, rather than the more normal one link.

Eicosanoid - Generic term for metabolic oxygenation product of twenty carbon polyunsaturates; see also prostaglandins and leukotrienes.

Eicosapentaenoic Acid (EPA) 20:5n-3, 20:5w3 - One of the two major omega-3 polyunsaturated fatty acids found abundantly in fish oils. It has a carbon chain with twenty carbon atoms and five double bonds at carbons 5, 8, 11, 14 and 17, so that the last one is at the 3rd carbon from the terminal methyl end.

Eicosatrienoic Acid (ETA) 20:3n-9, 20:3w9 - A polyunsaturated fatty acid with a carbon chain of twenty carbon atoms and three double bonds at carbons 5, 8 and 11, so that the last one is at the 9th carbon from the terminal methyl end. It is also known as Mead Acid; it can be synthesised by mammals, but is normally only found under conditions of severe EFA deficiency. It is thought that Mead Acid is the body’s attempt to mitigate the functional consequences of EFA deficiency. An isomer of 20:3n-9 is 20:3n-3 (with the last double bond at the 3rd carbon from the methyl end) which is not so nutritionally relevant.

Essential Fatty Acids (EFA) – A group of polyunsaturated fatty acids which are necessary for health in mammals. They cannot be synthesised, so must be supplied in the diet. Two groups are recognised, omega 3 polyunsaturates and omega 6 polyunsaturates.

Fatty Acid - Organic molecules consisting of an aliphatic carbon chain of 6-32 carbon atoms, with a methyl group at one end of the chain and a carboxylic acid group (carbon number 1) at the other end. Commonly combined in groups of three, esterified to glycerol to form triacylglycerols, which form the bulk of edible oils and fats.

Gamma-linolenic acid (GLA) 18:3n-6, 18:3w6. Fatty acid with 18 carbon atoms and three double bonds at carbons 6, 9 and 12, so that the last one is at the 6th carbon from the terminal methyl end. It is found in a few vegetable oils.

Long chain (LC) - Refers to fatty acids with more than 18 carbon atoms in the chain.

Leukotrienes - Group of powerful biological regulators, produced from 20 carbon precursors, mainly AA, initially by the action of the 5-lipoxygenase enzyme.

Linoleic acid: (LA) 18:2n-6, 18:2w6. Fatty acid with eighteen carbon atoms and two double bonds at carbons 9 and 12, so that the second one is at the 6th carbon from the terminal methyl end. It is a major fatty acid of vegetable oil.

Lipid - Organic molecules that are insoluble in water, but soluble in non-ionic solvents such as ethers, alcohols, etc. Common examples would be fatty acids, cholesterol, phospholipids.

Monoglyceride - (monoacylglycerol) Glycerol molecule with one of the three hydroxyl groups esterified to a fatty acid.

Oleic Acid (OA) 18:1n-9, 18:1w9 – Fatty acid with eighteen carbon atoms and one double bond at carbon 9, so that it is at the 9th carbon from the terminal methyl end. It is found in many vegetable oils with the highest proportion in olive oil.

Omega 3 (w 3 or n-3) – Convention used to number the carbon atoms in a fatty acid chain from the terminal methyl end. Thus omega 3 pufas have the last double bond located at the 3rd carbon from the methyl end. The remaining double bonds follow sequentially with one CH2 between them.

Omega-6 (w6, n-6) - Same as omega-3, but with the last one is at the 6th carbon from the methyl end.

Omega-9 (w9, n-9) - Same as omega-3, but with the last one is at the 9th carbon from the methyl end.

Omega 6 / omega 3 ratio – Ratio of the sum of all the omega 6 polyunsaturates in the diet, compared to the sum of all the omega 3 polyunsaturates in the diet. The ratio has a marked influence on the extent to which either family of polyunsaturates is further metabolised. Both families are metabolised by the same enzymes. This being the case, a large excess of one will inhibit the metabolism of the other family.

Pufa - Shorthand notation for polyunsaturated fatty acid.

Phospholipid -Either a glycerol molecule esterified by two fatty acids and a phosphoric acid linked to a hydrophylic alcohol, or a sphingosine molecule N-linked with one fatty acid, and esterified by a phosphoric acid linked to choline

Polyunsaturate(s) - Synonym for polyunsaturated fatty acid(s).

Prostaglandins (Prostanoids) - Group of powerful biological regulators, produced from 20 carbon precursors, mainly AA, initially by the action of the cyclo-oxygenase enzymes.

Short chain (sc) – Refers to fatty acids with 6 to 12 carbon atoms in the chain.

Triglyceride (Triacylglycerol) - Glycerol molecule with the three hydroxyl groups esterified by fatty acids.