The term disaccharide refers to a molecule formed by the covalent linking of two monosaccharides. Monosaccharides are simple sugars, such as glucose and fructose, which are the building blocks of carbohydrates. When two monosaccharides are joined together, they form a disaccharide. The most common disaccharides include sucrose (table sugar), lactose (found in milk), and maltose (formed by the breakdown of starch). Disaccharides are important sources of energy for the body and are found in a variety of foods, including fruits, vegetables, and grains.