Fats covered approximately 22% of energy requirements in diets of ancient human being, and simultaneously the value of ratio of polyunsaturated fatty acids (PUFA) to saturated (SFA) was estimated as 1.4 and the proportion of PUFA omega 6 to PUFA omega 3 was 1:1. During the last twenty thousands years the composition of human diets was changing dramatically due to economical, culture and social changes. However, there are indicators that the ratio of PUFA omega 6 to PUFA omega 3 in human diet was unchanging until beginning of XIX century. Dramatic technological breakthrough in food technology during last 100 years caused radical changes in the structure and quality of food consumption. It is estimated that at present fats cover about 40% of energy requirements in diets of people in developed countries, and the value of ratio of dietary PUFA omega 6 to PUFA omega 3 is 25:1 and even 50:1. Epidemiological nutritional studies indicate that in populations which consume inadequate amount of PUFA omega 3 most often occur the disorders on atherosclerotic and immunological background as compared to populations which consume diets with appropriate covering the requirements of dietary PUFA omega 3. Therefore, it could be supposed that increased occurrence so-called civilization disorders is the result of increased consumption of highly manufactured food with changed composition (and also to increased fats consumption and decreased consumption of PUFA omega 3). This hypothesis is confirmed by the observations that the supplementation of diets with PUFA omega 3 gives the desirable results in the treatment of many disorders. The main objective of this two parts paper is to characterize the polyunsaturated fatty acids, their metabolic path ways as well as the possibilities of the use of the diet supplementation with PUFA omega 3 in the treatment and prophylaxis of some metabolic disorders. The structure, sources, determination and pathways in organism are discussed in part I, and the role of eicosanoids originating from respective PUFA omega 3 and advantages of the supplementation the diet with PUFA are discussed in part II.