Trans fatty acids are the main cause of heart and neuronal diseases. It raises LDL and decrease HDL as well. Hence can induce atherosclerosis. Be cautious of this silent killer!! unsaturated fatty acid are not known as trans. They contain Cis isoform and omega 9 are known to be beneficial for heart. Hydrogenation of PUFA can introduce trans fatty acid.
Is a form of unsaturated fatty acids the other one is -cis (the good one) -trans fatty acids are metabolised in smaller compounds which are toxic (ex: acrylic aldehyde, acrylamide, etc) on manny levels in varrious tissues, also theirs esters are not suitable too in cells.
Hence the necessity of an intake of Omega-3 or better a good report between Omega-3 Omega-6 and Omega-9 highly balance in favor of Omega-3 6:2:1 or so..., In Paleolitic this was the report between them in an 'instinctive' empirical way, but with fire use and processing of food (industrialy in particular!) the report was inversed, and in latest 100year or so the effects are more than vissible!