Lactose is the main carbohydrate found in milk and dairy products and is digested by the enzyme lactase into its absorbable components - glucose and galactose - which are then used as fuel by the body.
Lactose maldigestion occurs when insufficient amounts of the enzyme lactase are available in the gut to digest lactose. This results in undigested lactose passing into the large intestine where it can be fermented by the bacteria in the colon and may cause unpleasant gastrointestinal symptoms in some individuals, such as flatulence, diarrhoea and abdominal pain.
Lactose intolerance is the occurrence of these symptoms, in people with clinically diagnosed lactose maldigestion, after consumption of lactose (as it is important to note that not everyone with lactose maldigestion will experience intolerance symptoms).
Lactose intolerance is a genetically determined condition, and several different types exist:
Congenital lactase deficiency
Interestingly, most people produce sufficient amounts of lactase at birth and during childhood to digest normal amounts of dietary lactose.
Occasionally infants are born without the ability to produce any lactase at all. This is known as congenital lactase deficiency and becomes apparent after the first exposure to breast milk.
This type of lactose intolerance is extremely rare with only 40 cases ever reported, but it can only be treated by complete exclusion of lactose from the diet for life.
Primary lactase deficiency
In some people, lactase production will begin to decline at some point after weaning, usually at about 2-3 years of age.
In these individuals, production of lactose usually stops during childhood or occasionally may continue into adolescence before stopping completely.
This is known as primary lactase deficiency and is usually treated by careful control of lactose intake in the diet.
Secondary or acquired lactase deficiency
This occurs in people who normally produce sufficient levels of lactose, but have suffered damage to the lining of the intestine, from which lactose is usually produced.
Common causes of damage include food poisoning or conditions such as coeliac disease (caused by allergy to gluten).
This type of lactase deficiency is usually reversible after the individual has recovered from the original cause.
Familial lactase deficiency
This is a genetically inherited condition where newborn babies are born with the ability to produce a substantial amount of lactase, but the enzyme does not work and cannot break down the lactose. Complete avoidance of lactose in essential from birth.