If there is just one double bond then it is monounsaturated. If there is more than one then it is polyunsaturated. Most fats contain a proportion of each of these three basic types of fatty acid but are generally described according to which type predominates. Saturated fats tend to be animal fats and are solid at room temperature. Butter, lard, suet and meat fat are saturated fats.
Unsaturated fats are liquid at room temperature.
They are usually of plant origin, though fish oils may also be high in polyunsaturated fatty acids. Plant oils may be hardened by the addition of hydrogen atoms, converting double bonds to single bonds. This process is known as hydrogenation. Hydrogenated vegetable oils are often present in margarine and other processed foods. Fats have a number of important functions in the body.