Lactose intolerance is the inability to fully digest the lactose in milk and other dairy products. This occurs when the body does not produce enough lactase enzymes to digest the amount of dairy eaten.
Lactose is a complex sugar (disaccharide) found in all dairy products, such as milk, ice-cream, butter, cheese, yoghurt, breast milk and some infant formulas. Lactase is the digestive enzyme which breaks down lactose into the simple sugars (monosaccharides) glucose and galactose which can then be absorbed through the intestinal lining.
The level of lactase enzymes manufactured in the body varies between individuals. A deficiency of the enzyme leads to the symptoms of lactose intolerance. When this happens the lactose in food moves undigested into the colon instead of being processed and absorbed. The undigested lactose interacts with normal bacteria in the colon producing lactic acid and hydrogen gas – resulting in abdominal discomfort, bloating, excess wind or gas and sometimes diarrhoea.
Lactose intolerance can affect people of all ages – from premmie babies to the elderly. In fact, it is very common among babies with immature digestive systems (see links between Colic and lactose intolerance), among certain ethnic races, and the elderly.
Lactose intolerance is not a milk or dairy allergy, which is an immune system response to cow’s milk proteins. Dairy allergies occur in only 4% of the population, primarily in infants and young children (see Key differences between lactose intolerance and dairy allergies).
Lactose intolerance may also be called lactase deficiency, lactose malabsorption, lactose overload or hypolactasia.