Lactose Intolerance - Terminology

Terminology

"Lactose intolerance" primarily refers to a syndrome having one or more symptoms upon the consumption of food substances containing lactose. Individuals may be lactose intolerant to varying degrees, depending on the severity of these symptoms. "Lactose malabsorption" refers to the physiological concomitant of lactase deficiency (i.e., the body does not have sufficient lactase capacity to digest the amount of lactose ingested). A medical condition with similar symptoms is fructose malabsorption.

Lactase deficiency has a number of causes and is classified as one of three types:

• Primary lactase deficiency is genetic, only affects adults and is caused by the absence of a lactase persistence allele. It is the most common cause of lactose intolerance as a majority of the world's population lacks these alleles.
• Secondary, acquired, or transient lactase deficiency is caused by an injury to the small intestine, usually during infancy, from acute gastroenteritis, diarrhea, chemotherapy, intestinal parasites or other environmental causes.
• Congenital lactase deficiency is a very rare, autosomal recessive genetic disorder that prevents lactase expression from birth. It is particularly common in Finland. People with congenital lactase deficiency are thus unable to digest lactose from birth, and they are unable to digest breast milk.

Lactose intolerance is not an allergy, because it is not an immune response, but rather a problem with digestion caused by lactase deficiency. Milk allergy is a separate condition, with distinct symptoms that occur when the presence of milk proteins trigger an immune reaction.