Lactose intolerance is the inability to digest lactose, the carbohydrates in milk. It is caused by the deficiency of the enzyme lactase, and consuming dairy products when you're lactose intolerant results in abdominal pain, bloating, gas and diarrhea. According to the International Foundation for Functional Gastrointestinal Disorders, lactose intolerance affects 20 percent to 60 percent of the U.S. population. The worldwide incidence varies with ethnicity, affecting very few people from Northwest Europe but is extremely high in people from Southeast Asia.
Cause of Lactose Intolerance
Produced by the cells in the small intestine, the enzyme lactase splits lactose in milk into its monosaccharide units of glucose and galactose. If you are lactose intolerant, a deficiency of lactase allows undigested lactose to reach the large intestine where the bacteria break it down. This causes symptoms of lactose intolerance such as bloating, flatulence and abdominal pain. The type of lactose intolerance that you have determines if the lactase activity is reversible.
Congenital Lactose Intolerance
Although extremely rare, some babies are born with an inability to produce lactase. These infants are unable to digest even the lactose in their mother's milk and suffer from diarrhea. Children who have this inherited form of lactose intolerance need to be on a lactose-free formula, as the enzyme activity is irreversible.
Primary Lactose Intolerance
In the early years of life, you produce sufficient amounts of lactase to digest the main diet of milk. However, when other foods replace milk, lactase production diminishes in response to decreased need. Over time, you may be unable to digest milk or dairy products. Every person responds to lactose intolerance in a different manner and some people may have a complete inability to digest milk. On the other hand, many adults who have primary lactose intolerance are able to consume small amounts of milk and dairy products.
Secondary Lactose Intolerance
Gastrointestinal diseases such as celiac disease, gastroenteritis or diarrheal illnesses may damage your small intestine and its ability to produce sufficient amounts of lactase, resulting in lactose intolerance. Secondary lactose intolerance is reversible, as lactase production may restart once the disease is treated.
References
- International Foundation for Functional Gastrointestinal Disorders; Lactose Intolerance: Definition, Symptoms and Treatment; September 2007
- MayoClinic.com; Lactose Intolerance; February 16, 2010
- "Alimentary Pharmacology & Therapeutics"; Review Article: Lactose Intolerance in Clinical Practice -- Myths and Realities; M.C.E.Lomer et al.; January 2008
- "Postgraduate Medical Journal"; Systemic Lactose Intolerance: A New Perspective on an Old Problem; S.B. Matthews et al.; March 2005
