EN
Trans-isomers of unsaturated fatty acids are formed in fairly great amount in the process of hydrogenation of fats, e.g. in hydrogenated rapeseed oil they account for about 60«/o of the total number of double bonds. Therefore margarines and other vegetable oils of solid consistence containing plant oils partly hydrogenated contain lower or higher level of thesse isomers.The role of trans-isomers in human nutrition has not yet been fully elucidated. The early studies on the nutritional value of these acids demonstrated that they produce no pathological changes in experimental animals, on condition that the diet contains a sufficient amount of essential unsaturated fatty acids in the cis form. If this is not the case, syptoms characteristic of deficiency of these essential fatty acids may develop since it is known that these acids changing to the trans form lose the biological properties of essential acids. Trans-isomers were found to be absorbed and used-up in the organism as a source of energy, similarly as the cis-isomers. The metabolism of trans-isomers is not well konwn yet. They are thought to undergo metabolic processes rather as saturated acids not as cis-unsaturated fatty acids. Trans-isomers of fatty acids were observed to interfere specifically with the metabolism of unsaturated fatty acids, that is they can inhibit the activity of delta-5-desaturase and delta-6-desaturase enzymes that participate in the metabolism of essential unsaturated fatty acids from the n-6 and n-3 groups what may lead to reduction of arachidonic acid level in tissues. Trans-isomers may replace linoleic and linolenic acids as substrates for desaturation and elongation of the carbon chain, and this way atypical compounds may be produced. These compounds after incorporation into cell membranes may affect their physiological functions. Atypical compounds may also be formed, which differ from those which are normal precursors of eicosanoids. This finally leads to formation of eicosanoids of changed structure. In the lipids of human tissues neither arachidonic acid, nor any other long- -chain polyunsaturated fatty acids containing double bonds in the trans configuration has been found. However, in the lipids of the tissues of rats receiving these isopiers in diet raised amount of arachidonic acid with trans bonds was found. In in vitro experiments considerable biochemical differences between various trans-isomers were demonstrated, and the position of the double bond was found to play possibly an important role. Each trans-isomer (geometric) of a polyunsaturated fatty acid may occur in several configurations, moreover, all these isomers of monounsaturated as well as polyunsaturated fatty acids are also position isomers (changed position of one or more double bonds). This influences the affinity of the enzymes to various isomers. This problem remains as yet to be explained. Since a long time trans-isomers have been known to be incorporated after ingestion into the lipids of human and animal tissues. They can be transported from the mother to fetal tissues or into milk. The effect of trans-isomers incorporated into the lipids of biological membranes on the metabolic processes was studied. It was found that they had no effect on the synthesis of eicosanoids in blood platelets and in aortic wall segments despite reduced content of arachidonic acid in cell membranes. They have also no influence either on the functions of hepatic mitochondria or cardiac mitochondria despite evident changes in the composition of fatty acids in the mitochondrial membranes in these organs. It is considered that adequate quantity of linoleic acid in the diet prevents the adverse effects of trans-isomers. According to some authors, it amounts at least to 2% of the total energy intake. The arising question is if there is a correlation between the ingestion of trans-isomers and the development of atherosclerosis. However, the opinions on the effect of the diatery trans-isomers on serum cholesterol content in humans and animals and on the prevalence and severity of atherosclerotic lesions are controversial. As yet the role played by trans- -isomers incorporated into the myocardial lipids has not been explained, especially in the condition of increased myocardial requirements for energy which is derived from fatty acids in 60—90%. Recently attention has been called to the possible correlation between the amount of trans-isomers in diet and morbidity and mortality from neoplastic diseases. According to one hypothesis trans-isomers causing changes in the composition of fatty acids in cell membranes produce changes in their function leading ultimately to neoplastic proliferation of certain tissues. The effect of dietary trans-isomers of fatty acids on human organism is still an open question requiring further studies. Opinions on the biological value of fats containing these isomers presented by various authors are controversial.