**2.1. Fatty acids**

Fatty acids are classified as saturated fatty acid (SFA), monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA). The essential fatty acids (EFAs) refer to those polyunsaturated fatty acids (PUFAs) that must be provided in our food because these EFAs cannot be synthesized in our body, and they are necessary for a good health. The main two families of EFAs are omega-3 (ω-3) and omega-6 (ω-6). ω-3 and ω-6 structures are based on the position of the double bond from the methyl (omega) terminal of the aliphatic carbon chain [1, 15]. The parent fatty acid of the ω-6 series is linoleic acid (18:2n-6) and the parent fatty acid of the ω-3 series is linolenic acid (18:3n-3.). ω-3 includes alpha-linolenic acid (ALA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) (**Figure 1**).

Human body can synthesized omega-3 and omega-6 from linoleic acid and linolenic acid, respectively, through a series of desaturation (addition of a double bond) and elongation (addition of two carbon atoms) reactions [16]. Unlike linolenic and linoleic acid, oleic acid (18:1n-9) is consumed in substantial amounts in the Western diet and is not an essential fatty acid. There is a little eicosatrienoic acid (ETA, 20:3n-9) in cell membranes, however, probably because of the overwhelming competition from dietary linoleic acid for the relevant desaturase and elongase enzymes. The pathways for desaturation and elongation of ω-3 and ω-6 fatty acids are given in **Figure 2**.
