Explain the term Trans fatty acids?

Plant derived fats and oils contain cis-fatty acids. You may recall reading about the cis and trans isomers in the Nutritional Biochemistry Course. Cis and trans-isomers, we learnt, have the same chemical formula but different chemical structure and properties. Trans-fatty acids are produced when vegetable oils are hydrogenated to make margarines, partially hydrogenated vegetable shortening and vanaspati. Hence, major sources of trans-fatty acids to human diets are commercially baked products, deep fried snacks in vanaspati and mithai. Small amount of trans-fatty acids are present in milk fat formed by bacterial conversion of cis into trans-fatty acids in cow's stomach. Metabolically, trans-fatty acids and saturated fatty acids raise blood cholesterol levels.