Gastroenterology clinic

Lactose intolerance

Sue Shepherd



The severity of the common symptoms of lactose intolerance (diarrhoea or loose motions, wind and abdominal pain, bloating and discomfort) depends on the level of lactase insufficiency in an individual. Most affected patients have some persisting lactase activity and are able to tolerate small amounts of lactose.

Article Extract

  • Lactose is a disaccharide that naturally occurs in milk derived from mammals, including cows, sheep and goats. It is made up of the two monosaccharides glucose and galactose, and requires hydrolysis by the enzymic action of lactase for its absorption.
  • Lactase enzyme is secreted by epithelial cells lining the small intestine. Causes of lactase insufficiency may be congenital (very rare), primary or secondary. Primary, or ‘delayed onset’, lactase insufficiency affects more than half of the world’s population, particularly non-Caucasian populations, including Asians, Southern Europeans and Aboriginals. About 90% of Asian people are affected, compared with an estimated 10% of people of Caucasian descent. Secondary deficiency may occur due to co-existing or recent giardiasis, viral infections, coeliac disease, bacterial overgrowth or Crohn’s disease.