They perform better in certain uses, such as when creaming a cake batter. Fats with a higher level of unsaturated fats tend to be liquid at room temperature. They may be more useful in other recipes, such as when making salad dressings. Although they may be solid, most shortening and margarine products are made from liquid vegetable oils that have been partially hydrogenated. These products are hydrogenated only as much as needed to produce the desired texture and taste.
Hydrogenation increases the firmness and melting point of oils.
Partially hydrogenated products still contain more unsaturated than saturated fats. Trans fats are produced when unsaturated fats and oils are partially hydrogenated. They also occur naturally in small amounts in meats and dairy products. Trans fats make up a small percentage, between two and three percent, of the total fat intake in the average American diet. The fats that we get from food are vital to good health.