Dietary lactose and the aetiology of human small-intestinal hypolactasia.

The only carbohydrate in milk is lactose, a disaccharide, which is formed of a molecule of glucose and a molecule of galactose. Cow's milk contains about 5 % lactose and human milk about 6'5-7 %. Lactose is hydrolysed to its monosaccharides principally by a specific enzyme, lactase, which is a f-galactosidase. There are also two other enzymes with ,3-galactosidase activitv, lysosomal acid 3-galactosidase and cytoplasmic hetero-/-galactosidase, but their role in the hydrolysis of lactose is very small'. The latter has only in vitro activity.