lactose

Meaning of lactose: Lactose is the natural sugar in milk that requires the enzyme lactase to be broken down and absorbed in the intestine.

Definition of lactose

Lactose is a sugar found naturally in milk and dairy products, formed from two smaller sugar units joined together. To be absorbed, lactose must first be broken down in the small intestine by an enzyme called lactase, which splits it into its two simpler sugar components.

When lactase activity is reduced or absent, undigested lactose passes into the lower intestine, where it can be fermented by bacteria and draw in fluid, producing symptoms such as bloating, gas, cramping, and diarrhea, a condition known as lactose intolerance. Lactase levels commonly decline with age in much of the world's population, though the timing and extent vary widely between individuals and populations.

Lactose intolerance is distinct from a milk allergy, which involves an immune reaction to milk proteins rather than a difficulty digesting a sugar.