Digestive System Home > Lactose Intolerance

When a person is unable to digest lactose (the major sugar found in milk), this is known as lactose intolerance. The cause of the condition is a shortage of the enzyme lactase within the body. Common symptoms include cramps, bloating, gas, and diarrhea. In many cases, modifying your diet will improve the symptoms of lactose intolerance.

An Introduction to Lactose Intolerance

Lactose intolerance is the inability to digest significant amounts of lactose (the major sugar found in milk).
People sometimes confuse lactose intolerance with cow's milk intolerance because the symptoms are often the same. However, the two conditions are not related. Being intolerant to cow's milk is an allergic reaction triggered by the immune system. Lactose intolerance is a problem caused by the digestive system.

What Is Lactose Intolerance?

Lactose intolerance is a condition that results from a deficit of lactase (lactase deficiency), an enzyme produced by the cells lining the small intestine. Lactase is necessary to digest lactose, the natural sugar found in milk. Lactase breaks down lactose (milk sugar) into two simpler forms of sugar called glucose and galactose, which are then absorbed into the bloodstream. When there is a shortage of lactase, the body is not able to break down lactose, and it travels through the intestines unchanged. In the intestines, undigested lactose has a laxative effect and stimulates the growth of bacteria that produce significant amounts of gas. Within 30 minutes to 2 hours after ingesting lactose, abdominal cramping and diarrhea often occur. These symptoms are essential to a diagnosis of lactose intolerance.
Not all people with lactase deficiency have the symptoms commonly associated with lactose intolerance, but those who do are said to have lactose intolerance.
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Last reviewed by: Arthur Schoenstadt, MD
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