Figure 1. Nomenclature for fatty acids. Fatty acids may be named according to systematic or trivial nomenclature. One systematic way to describe fatty acids is related to the methyl () end. This is used to describe the position of double bonds from the end of the fatty acid. The letter n is also often used to describe the position of double bonds.

Figure 2. Structure of different unbranched fatty acids with a methyl end and a carboxyl (acidic) end. Stearic acid is a trivial name for a saturated fatty acid with 18 carbon atoms and no double bonds (18:0). Oleic acid has 18 carbon atoms and one double bond in the -9 position (18:1 -9), whereas eicosapentaenoic acid (EPA), with multiple double bonds, is represented as 20:5 -3. This numerical scheme is the systematic nomenclature most commonly used. It is also possible to describe fatty acids systematically in relation to the acidic end of the fatty acids; symbolized (Greek delta) and numbered 1. All unsaturated fatty acids are shown with cis configuration of the double bonds. DHA, docosahexaenoic acid.

Figure 3. Synthesis of -3 and -6 polyunsaturated fatty acids (PUFAs). There are two families of essential fatty acids that are metabolized in the body as shown in this figure. Retroconversion, e.g. DHAEPA also takes place.

Figure 4. Metabolism of fatty acids. Free fatty acids (FFA) are taken up into cells mainly by protein carriers in the plasma membrane and transported intracellularly via fatty acid-binding proteins (FABP). FFA are activated (acyl-CoA) before they can be shuttled via acyl-CoA binding protein (ACBP) to mitochondria or peroxisomes for -oxidation (formation of energy as ATP and heat), or to endoplasmic reticulum for esterification to different lipid classes. Acyl-CoA or certain FFA may bind to transcription factors that regulate gene expression or may be converted to signalling molecules (eicosanoids). Glucose may be transformed to fatty acids if there is a surplus of glucose/energy in the cells.

Figure 5. Mechanisms of action for fatty acids. Thromboxanes formed in blood platelets promote aggregation (clumping) of blood platelets. Leukotrienes in white blood cells act as chemotactic agents (attracting other white blood cells). See Figure 7.

Figure 6. Synthesis of eicosanoids from Arachidonic acid or eicosapentaenoic acid (EPA).

Figure 7. Biological effects of eicosanoids derived from Arachidonic acid (AA; 20:4 -6) or eicosapentaenoic acid (EPA; 20:5 -3). TX, thromboxane; PG, prostaglandin, LT, leukotriene.

Figure 8. Advice for dietary lipid sources and amounts.