Omega-3 polyunsaturated fatty acids and behavior

Humans typically consume about 20 different types of fatty acids in the diet, which can be grouped as either saturated or unsaturated fatty acids. Saturated fatty acids have single bonds between the carbon atoms and are rigid in nature. Unsaturated fatty acids may have one (monounsaturated) or more (polyunsaturated) double bonds and the position of the rst double bond in relation to the omega end determines whether a polyunsaturated fatty acid is termed an omega-3 (n-3) or an omega-6 (n-6) fatty acid. Mammals are capable of manufacturing every fatty acid required for biological processes except for two; namely linoleic acid (LA, n-6) and α-linolenic acid (ALA, n-3). These are termed the “essential” fatty acids and must be acquired via the diet (Simopoulos 2000). LA and ALA are sometimes referred to as “parent” fatty acids as it is from these that their respective long-chain biologically active metabolites are derived. Arachidonic acid (AA, n-6) is the major metabolite of LA, whereas eicosapentaenoic acid (EPA, n-3) and docosahexaenoic acid (DHA, n-3) are the major metabolites of ALA (Figure 8.1). AA, EPA, and DHA are synthesized from their respective precursor parent fatty acids by a series of elongations and desaturations that, despite the fact that the conversion pathways for n-6 and n-3 fatty acids are entirely independent, require the same enzymes at each step. There is also some evidence to suggest that DHA can be “retro-converted” into EPA, although rates of only 20% have been observed (Gronn et al. 1991). The metabolism of LA and ALA is predominantly carried out in the endoplasmic reticulum of the liver, in certain structures in the central nervous system such as glial cells (Moore 2001) and the choroid plexus vasculature (Bourre et al. 1997), and has also been observed at low rates in the placenta (Haggarty 2004).