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 bloodstream 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.