Oils and fats form an important part of a healthy diet. Structurally they are esters of glycerol with three fatty acids (called either triacylglycerols or triglycerides). It is these fatty acids that give the functionality to fats. Chemically, they can be divided into four main types – saturated, cis-monounsaturated, cis-polyunsaturated and trans fatty acids. In very broad terms, saturated fatty acids and trans fatty acids are solid at room temperature while the cis-unsaturates are liquid at room temperature. Although no naturally occurring fat is either 100% saturated or 100% unsaturated (but is a mix of the two), fats are often referred to as ‘saturated’ or ‘unsaturated’ because of the predominance of one or other type of fatty acid.