Lactose

Reader's Guide

Lactose is significant as the primary sugar in mammalian milk, providing energy to infant mammals. Its digestion requires the enzyme lactase, which is produced in the small intestine. In many human populations, especially those with ancestry in Europe, West Asia, South Asia, and parts of Africa, lactase production persists into adulthood due to genetic selection, allowing continued consumption of milk. Lactose intolerance occurs when lactase is insufficient, leading to gastrointestinal symptoms.

Industrially, lactose is purified from whey, a byproduct of cheese production, and used as a carrier and stabilizer in pharmaceuticals and foods, notably infant formula. It is also used to sweeten stout beer (milk stout) and can be fermented by Kluyveromyces yeast for ethanol production. Its low cariogenicity and positive effects on mineral absorption are notable biological properties. The history of its isolation and naming spans from the 17th to 19th centuries, involving several prominent scientists.

Did You Know?

• Lactose makes up around 2–8% of milk by mass, with bovine milk at about 4.8% and rhesus macaque milk at 8%.
• Lactose has a sweetness of 0.2 to 0.4 relative to sucrose, and a glycemic index of 46 to 65.