Lactose

Lactose is a complex sugar found in large amounts in milk.

Structure of lactose

Lactose is a disaccharide, i.e. it is a complex sugar, made up of an association of two simple sugars, glucose and galactose, connected by a specific carbohydrate bond (hence its official name of β-D-galactopyrannosyl(1→4)D-glucopyrannose). Its elemental chemical formula is C₁₂H₂₂O₁₁.

Function of lactose

Lactose is found in high concentrations in mammal milk and is an important nutritional energy source. It is converted into glucose and galactose in the infant gastrointestinal tract by the enzyme β-galactosidase (a lactase). These molecules are then absorbed separately.

Lactose intolerance

Although it is found in all mammal babies, this enzyme may be deficient in some adults causing lactose intolerance. In this case lactose is no longer broken down into simple sugars and cannot be absorbed but remains in the gastrointestinal tract. It is the metabolised by intestinal bacteria (producing hydrogen, methane and carbon dioxide) which causes intestinal discomfort and even diarrhoea.