Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: February 14, 2004
Publication Date: March 20, 2006
Citation: Heird, W.C. 2006. The role of essential fatty acids in development. In: Thureen, P., Hay, W., editors. Neonatal Nutrition and Metabolism. 2nd edition. New York, NY: Cambridge University Press. p. 147-160. Technical Abstract: Fatty acids are aliphatic monocarboxylic acids. They are classified as saturated, monounsaturated, or polyunsaturated fatty acids depending upon the number of double bonds in the carbon chain. Saturated fatty acids have no double bonds, monounsaturated fatty acids have 1 double bond, and polyunsaturated fatty acids have 2 or more, but usually no more than 6, double bonds. Most fatty acids can be synthesized endogenously, but the major source is from dietary fat which accounts for approximately half the energy content of breast milk and infant formulas. Triglycerides, which have three, usually different, fatty acid molecules esterified to a molecule of glycerol, are the major components of dietary fat; the remainder includes phospholipids, monoglycerides, diglycerides, and sterols. These are hydrolyzed in the intestinal lumen, the released fatty acids are reassembled within the enterocyte and the reassembled triglycerides, phospholipids, monoglycerides, and sterol esters are absorbed primarily into the thoracic duct from which they eventually reach the blood stream where they circulate as components of the various lipoproteins. Some free fatty acids also are absorbed and circulate bound to albumen. All fatty acids have common names, but, by general convention, they are identified by a "shorthand" system indicating their number of carbon atoms, their number of double bonds, and the site of the first double bond from the terminal methyl group of the molecule. For example, palmitic acid, a 16-carbon saturated fatty acid is designated 16:0, and oleic acid, an 18-carbon monounsaturated fatty acid with its single double bond located between the ninth and tenth carbon from the methyl terminal, is designated 18:1 omega-9. Linoleic acid (LA) and alpha-linolenic acid (ALA) are designated 18:2 omega-6 and 18:3 omega-3, respectively. Both are 18-carbon polyunsaturated fatty acids. LA has 2 double bonds, the first between the sixth and seventh carbon from the methyl terminal, and ALA has 3 double bonds, the first between the third and fourth carbon from the methyl terminal.