Novije medicinske spoznaje pokazuju da u razvoju krvožilnih i drugih kroničnih bolesti kod ljudi značajnu ulogu ima međusobni odnos dviju skupina polinezasićenih masnih kiselina u prehrani: omega-6 kiselina čiji je osnovni predstavnik linolna kiselina (C18:2 n-6) i omega-3 kiselina, čiji je osnovni predstavnik alfa linolenske kiselina (C18:3 n-3). U organizmu, procesima elongacije i desaturacije iz LA nastaju ostale n-6 kiseline, poput arahidonske kiseline (AA, C20:4 n-6), dok iz ALA nastaju dugolančane n-3 kiseline, kao što su eikosapentaenoična (EPA, C20:5 n-3) i dokosaheksaenoična kiselina (DHA, C22:6 n-3). Polinezasićenih masnih kiselina sa 20 C atoma predkursori su eikosanoida, koji kao tkivni hormoni (prostaglandini, tromboksani i leukotrieni) s lokalnim nastajanjem i djelovanjem u tkivima reguliraju različite fiziološke procese, poput grušanja krvi i upalne reakcije. Eikosanodi koji nastaju iz kiselina različitih n-skupina imaju različitu strukturu i biološke učinke u tkivima. Tako tromboksan A2, koji nastaje iz AA (C20:4 n-6) izaziva nakupljanje trombocita i grušanje krvi a u patološkim okolnostima trombozu, dok iz EPA (C20:5 n-3) nastaje trombogeno neaktivni tromboksan A3. Slično tome, leukotrieni koji nastaju iz AA imaju snažnije pro-upalno djelovanje od onih koji nastaju iz EPA. Razine navedenih eikosanoida ovise o količinama AA (C20:4 n-6) i EPA (C20:5 n-3) u fosfolipidima tkivnih stanica, a njihove količine ovisi o relativnim količinama LA (C18:2 n-6) i ALA (C18:3 n-3) u prehrani. Količina LA u suvremenoj prehrani ljudi jako se povećala uporabom jestivih biljnih ulja koja sadrže visok udio LA, te mesa, jaja i ribe s povećanim sadržajem LA uslijed intenzivne hranidbe životinja žitaricama, također bogatom izvoru LA. Smatra se da je razvoj ljudskog roda tekao uz odnos n-6/n-3 u prehrani oko 1 do 2 dok je u prehrani današnjih ljudi taj odnos je značajno promijenjen i iznosi 10 do 20 i više. Gubitak ravnoteže n-6 i n-3 polinezasićnih masnih kiselina u prehrani povezuje se uz uzroke pojave i stalnog porasta bolesti moderne civilizacije. Istraživanja su pokazala da povećani unos n-3 masnih kiselina u hrani u odnosu na unos omega-6 masnih kiselina, može smanjiti rizik od razvoja krvožilnih, autoimunih i drugih kroničnih bolesti. Sukladno tome, zdravstvene organizacije savjetuju smanjenje omjera n-6/n-3 u svakodnevnoj prehrani.Recent medical researches indicated the significanceof the role of nutritional levels of omega-6 (n-6) and omega-3 (n-3) polyunsaturated fatty acids in the development of cardiovascular and other chronical diseases in humans. Principal n-6 fatty acid is linoleic (LA, 18:2 n-6) and principal n-3 fatty acid is alpha-linolenic acid (ALA, 18:3 n-3). In organism, these fatty acids can be elongated and desaturated into their longer-chain derivates such as arachidonic acid (AA, 20:4, n-6), derived from LA, or eicosapentaenoic acid (EPA, 20:5 n-3) and docosahexaenoic acid (DHA, 22:6 n-3), derived from ALA. Polyunsaturated fatty acids with 20 carbons in the chain act as precursors for eicosanoides include prostaglandins, leukotrienes and thromboxanes. These have an important role as regulators of many physiological processes in tissues, such as blood clotting or inflammatory response. Eicosanoides derived from polyunsaturated fatty acids of different n-series have a different structure and biological effects. Thus, tromboxane A2 produced from AA (20:4 n-6) is a powerful pro-aggregatory agent in heamostasis whereas tromboxane A3 produced from EPA (20:5 n-3) is much less active. Similarly, leukotrienes derived from AA (20:4 n-6) stimulate the inflammatory response more than those derived from EPA (20:5 n-3). The levels of these eicosanoides depend on the quantities of AA and EPA in the phospholipids of tissue cells, and these amounts, in turn, depend upon the relative amounts of their precursors, LA (18:2 n-6) and ALA (18:3 n-6) in the diet. The amount of LA (18:2 n-6) in modern diet has been increased considerably by the use of vegetable oils that contain high proportion of LA. Meat, eggs and fish from industrial production, als contai nhig hamount of LA because concentrate grain-based feeds are rich source of LA. It is believed that humans evolved with nutritional ratio of n-6/n-3 of 1-2 whereas in current diet this ratio has been significantl yincreased and ranges from 10 to 20 or more. Lost of balance of n-6 and n-3 polyunsaturated fatty acids in the diet has been linked with causes of permanent growth of modern civilization diseases. Researches showed that increased intake of n-3 polyunsaturated fatty acids in relation to intake of n-6 polyunsaturated fatty acids, may have beneficia leffects in the prevention of cardiovascular, autoimmune and other chronical diseases. In agreement with that, medical organizations recommended lowering n-6/n-3 ratio in daily nutrition
