Lactose Intolerance
Lactose intolerance is the inability to digest the sugar lactose (which is present in all dairy products) because of a deficiency of the digestive enzyme lactase, leading to diarrhea and abdominal cramping.
Between 30 million and 50 million people in the United States are lactose intolerant. Lactose, the predominant sugar found in milk and other dairy products, is broken down by the enzyme lactase, which is produced by the cells in the inner lining of the small intestine. Normally, the enzyme lactase breaks down lactose, a complex sugar, into its two components, glucose and galactose. These simple sugars are then absorbed into the bloodstream through the intestinal wall. If lactase is lacking, lactose cannot be digested and absorbed. The resulting high concentration of lactose draws fluid into the small intestine, causing diarrhea. The unabsorbed lactose then passes into the large intestine, where it is fermented by bacteria, resulting in flatulence and acidic stool.
Intolerances to other sugars can also occur but are relatively rare. For example, a lack of the enzyme sucrase prevents the sugar sucrose from being absorbed into the bloodstream, and a lack of the enzymes maltase and isomaltase prevents the sugar maltose from being absorbed into the bloodstream.
Symptoms
People with lactose intolerance usually cannot tolerate milk and other dairy products, all of which contain lactose. Some people recognize this early in life and consciously or unconsciously avoid dairy products.
A child who is lactose intolerant has diarrhea and may not gain weight when milk is part of the diet. An adult may have abdominal bloating, cramps, diarrhea, flatulence, nausea, audible bowel sounds (borborygmi), and an urgent need to have a bowel movement between 30 minutes and 2 hours after eating a meal containing lactose. For some people, severe diarrhea may prevent proper absorption of nutrients because they are expelled from the body too quickly. However, the symptoms that result from lactose intolerance are usually mild. In contrast, symptoms that result from malabsorption in such conditions as celiac disease, tropical sprue, and infections of the intestine are more severe.
Diagnosis and Treatment
A doctor suspects lactose intolerance when a person has symptoms after consuming dairy products. If a 3- to 4-week trial period of a diet free of dairy products eliminates the symptoms, the diagnosis is confirmed. Specific tests are rarely necessary.
Lactose intolerance can be controlled through diet by avoiding foods containing lactose, primarily dairy products. Lactase enzymes are available in liquid and tablet forms without a prescription and can be added to milk. Lactose-reduced milk and other products are available at many supermarkets. People who must avoid dairy products should take calcium supplements to prevent calcium deficiency.
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