Lactose

Lactose is a disaccharide sugar found primarily in the milk of mammals. It is composed of glucose and galactose linked by a beta-1,4-glycosidic bond. Lactose is produced by the mammary gland during milk synthesis and serves as a source of energy in early life and as a component of dairy products.

Digestion of lactose depends on the enzyme lactase, produced in the small intestine. In individuals with sufficient lactase activity, lactose is split into glucose and galactose, which are absorbed. In those with lactase deficiency or reduced lactase activity, lactose remains intact in the intestine and is fermented by colonic bacteria, producing gas and short-chain fatty acids that may cause bloating, abdominal pain, and diarrhea. The ability to digest lactose into adulthood, known as lactase persistence, varies by population due to genetic differences.

In foods, lactose content varies with processing. Fresh milk contains substantial lactose, while many aged cheeses and butter have lower levels due to concentration and removal during processing. Lactose-free dairy products are produced by adding lactase to milk, breaking lactose into glucose and galactose before consumption. The sugar is also used in the food industry as a fermentation substrate and as a sweetener in some processed foods.

Nutrition and health considerations: lactose contributes to carbohydrate energy intake and can aid mineral absorption in some contexts, but it can cause symptoms in lactose-intolerant individuals. Management options include consuming lactose-reduced dairy products or using lactase supplements, and relying on labeling to guide choices.