Lactose is a sugar (milk sugar) naturally found in milk and dairy products. It is a disaccharide that consists of the simple sugars galactose and glucose and has just as many calories as normal table sugar. Lactose is an important component of breast milk and a source of energy for infants. The enzyme lactase is required to break it down into glucose and galactose. Some people lack this completely or partially, which is why they suffer from lactose intolerance.
