Fatty Acids

Fatty acids can be present as triacylglycerol, as part of lipoprotein particles, and as free fatty acids (bound to albumin). Common fatty acids and their sources are listed in Table 2.

Fatty acids are straight-chain compounds of differing lengths connecting a hydrocarbon group to a hydroxyl group. With only single bonds in the straight chain, the fatty acid is saturated; with one or more additional double bonds, the fatty acid is unsaturated. Fatty acids with only one double bond are said to be monounsaturated (e.g., oleic acid, C18:1), whereas fatty acids with two or more double bonds are said to be polyunsaturated (e.g., ara-chidonic acid, C20:4). The presence of a double

Table 2 Fatty acids and their sources

Fatty acid

Structure Source

Saturated

Lauric

Palmitic

Stearic Behanic

Lignoceric Unsaturated

Oleic

Linoleic

Linolenic

Arachidonic

Eicosapentenoic

C12:0 C16:0

C18:0 C22:0

C24:0 C18:1

C18:2

C18:3 C20:4 C20:5

Coconut oil, palm kernel oil Palm oil, milk, butter, cocoa, butter, beef, pork, lamb

Some seed oils, especially peanut

Olive oil, most commonly occurring fatty acid Corn oil, soya bean oil, sunflower oil and sunflower seed oil Linseed oil Fish oils Cod, salmon, pilchard, mussel, oyster

44 63

69 80

84 11

11 50 54

Docosahexenoic C22:6

From Durrington PN (2004) Hyperlipidaemia: Diagnosis and Management. London: Hodder Arnold.

bond allows there to be two isomers, depending on whether the hydrogen atoms attached to the carbon atoms on either side of the double bond lie on the same side (cis) or opposing sides (trans). Cis isomers are the only naturally occurring isomers and form kinks in the fatty acid chain. Trans isomers occur as part of food processing and maintain the straight direction of fatty acid chains. The common saturated fatty acids are palmitic (C16:0) and stearic (C18:0) acids.

Diets rich in omega-3 polyunsaturated fatty acids (n-3 PUFAs), such as a-linoleic acid, eicosapentanae-noic acid, and decosahexaenoic acid, are associated with less coronary heart disease, and conjugated linoleic acids have beneficial effects against atherosclerosis. n-3 PUFAs function mainly by changing membrane lipid composition, cellular metabolism, signal transduction, and regulation of gene expression. It is postulated that receptors exist for fatty acids or their metabolites that are able to regulate gene expression and affect metabolic or signalling pathways associated with coronary heart disease. Three nuclear receptors are thought to be fatty acid receptors that respond to dietary and endogenous ligands: peroxisome proliferator activated receptors, retinoid X receptors, and liver X receptors.

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