Lactose Intolerance

What Is It?

Lactose intolerance is a common cause of abdominal cramping, bloating and diarrhea. This condition is caused by insufficient levels of the intestinal enzyme lactase, which breaks down lactose, the predominant sugar in milk, into simpler forms that can then be absorbed into the blood stream. When there is not enough lactase in the small intestine to digest the amount of lactose consumed, the undigested lactose rapidly passes into the colon. Bacteria in the colon then break down some of the lactose, producing hydrogen gas as a byproduct. The remaining lactose also draws water into the colon, causing diarrhea, bloating and flatulence.

The most common cause of lactose intolerance is the genetically determined reduction in lactase production that occurs at about age 5 in many people of African or Asian descent. As many as 90 percent of Asian-Americans, 80 percent of Native-Americans, 65 percent of African-Americans and 50 percent of Hispanics have some degree of lactose intolerance. In contrast, most Caucasians (80 percent) have a gene that preserves the ability to produce lactase into adulthood. There is also a rare syndrome of congenital lactase deficiency in which affected infants have a complete absence of lactase. Unable to digest lactose, the infants have diarrhea from birth. This condition usually was fatal before the development of lactose free infant formulas.

Lactose malabsorption can be caused by various gastrointestinal disorders. Viral or bacterial gastroenteritis and other diseases, such as celiac sprue, can destroy the lactase producing cells that line the small bowel. A condition called bacterial overgrowth, in which the small bowel contains higher than normal levels of bacteria, can cause lactose intolerance. The bacteria break down lactose in the small bowel, causing flatulence and diarrhea.

Symptoms

Common symptoms of lactose intolerance include watery, bulky odd smelling stools; nausea; abdominal pain; cramps; bloating; and flatulence that begin about 30 minutes to two hours after ingesting foods containing lactose. The severity of symptoms varies, depending on the amount of lactose an individual can tolerate, the amount of lactose ingested, and the size and fat content of the meal. People who also suffer from irritable bowel syndrome tend to have more severe symptoms from lactose intolerance.

Diagnosis

The diagnosis of lactose intolerance often is suggested when the gastrointestinal symptoms dramatically improve on a lactose free diet. In some cases, further testing is performed to establish the diagnosis.

The most commonly used test to confirm the diagnosis is the lactose breath hydrogen test. The test is painless and noninvasive. You cannot eat food for several hours beforehand.