The building blocks of sugar are called monosaccharides. Monosaccharides are simple sugars that cannot be broken down into smaller sugars. The most common monosaccharides are glucose, fructose, and galactose. Glucose is the body's main source of energy. Fructose is a natural sugar found in fruits and honey. Galactose is a component of the milk sugar lactose.

Monosaccharides can be linked together to form disaccharides and polysaccharides. Disaccharides are made up of two monosaccharides. The most common disaccharides are sucrose, lactose, and maltose. Sucrose is the common table sugar. Lactose is the sugar found in milk. Maltose is a sugar that is produced by the breakdown of starch.

Polysaccharides are made up of many monosaccharides. The most common polysaccharides are starch, cellulose, and glycogen. Starch is a storage form of glucose found in plants. Cellulose is a structural component of plant cell walls. Glycogen is a storage form of glucose found in animals.