A fat which is not fully saturated with hydrogen. Each molecule contains at least one double bond between two carbon atoms because these carbon atoms have not combined with all the hydrogen atoms they could carry. They are more reactive than saturated fats and combine relatively easily with oxygen to become rancid.
There are two main types of unsaturated fats: cis fats and trans fats. Cis fats have molecules with irregular shapes that do not allow them to pack closely together, consequently they are liquid at room temperature. Most natural vegetable oils contain cis fats. Trans fats form straight-chained molecules that can pack tightly together. Trans fats have properties similar to those of saturated fats, making them more harmful to health than cis fats. Butter, milk fat, and some vegetable oils that have been hydrogenated contain significant amounts of trans fats. See also monounsaturated fat and polyunsaturated fat.
Subjects: Medicine and Health.