Lactose is a type of disaccharide carbohydrate (sugar) found in animal breast milk, most commonly in cows milk but also found in other mammalian milk including human breast milk.  The digestive  enzyme lactase, found in our gut and used to digest (break down) dietary lactose into absorbable glucose and galactase, is often naturally switched off in certain communities after weaning. These communities are consequently unable to digest lactose and develop unpleasant symptoms as the lactose ferments in their bowels releasing hydrogen and methane gases causing bloating, flatulence, abdominal pain and diarrhoea within a few hours of ingesting cow’s milk. It is estimated that about half of all adults in the world have an element of lactose intolerance. This can be remedied by drinking lactose-free milk or mixing a lactase enzyme supplement called Colief with cow’s milk.

Lactose intolerance can be tested in 3 ways :

  1. Hydrogen breath test. After drinking cow’s milk, the lactose ferments and causes hydrogen gas to be released which can be measured in our breath.
  2. Lactose absorption test: Undigested lactose is not absorbed, so after a milk drink containing lactose, the blood glucose level does not go up as expected.
  3. Stool test for Faecal  Reducing Substances: The unabsorbed lactose ferments and makes the loose stools acidic and traces of lactose can be measured in the diarrhoea confirming lactose intolerance.

Reference:

Lomer MCE, Parkes GC, Sanderson JD. Review article: lactose intolerance in clinical practice‐‐myths and realities. Aliment. Pharmacol. Ther. 27: 93–103, 2008