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Medical Author:

Jay W. Marks, MD

Jay W. Marks, MD

Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

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Medical Editor:

Bhupinder Anand, MD

In this Article

• What is lactose intolerance?
• What causes lactose intolerance?
• What are the symptoms of lactose intolerance?
• How are lactase deficiency and lactose intolerance diagnosed?
• Elimination diet
• Milk challenge
• Breath test
• Blood glucose test
• Stool acidity test
• What are the sources of lactose in the diet?
• How is lactose intolerance treated?
• What are the long-term consequences of lactose intolerance?
• What is new in lactose intolerance?
• Lactose Intolerance At A Glance
• Patient Comments: Lactose Intolerance - Causes
• Patient Comments: Lactose Intolerance - Symptoms
• Find a local Gastroenterologist in your town
• Lactose Intolerance Index

A milk challenge is a simpler way of diagnosing lactose intolerance than an elimination diet. A person fasts overnight and then drinks a glass of milk in the morning. Nothing further is eaten or drunk for 3-5 hours. If a person is lactose intolerant, the milk should produce symptoms within several hours of ingestion. If there are no symptoms or symptoms are substantially milder than the usual symptoms, it is unlikely that lactose intolerance is the cause of the symptoms. It is important that the milk that is used is fat-free in order to eliminate the possibility that fat in the milk is the cause of symptoms. It is not possible to eliminate the possibility that symptoms are due to milk allergy, a very different condition than lactose intolerance; however, this usually is not confusing since allergy to milk is rare and primarily occurs in infants and young children. (If milk allergy is a consideration, pure lactose can be used instead of milk.)

An important issue is the amount of milk required for the milk challenge.

• If a person drinks several glasses of milk or ingests large amounts of milk-containing products in their normal diet, then a larger amount of milk should be used in the challenge, 8-16 ounces in an adult, equivalent to one or two large glasses of milk.

• If the person being tested usually does not drink several glasses of milk or ingest larger quantities of milk-containing products, there may be a problem with using 8-16 ounces of milk for testing. These larger quantities of milk used for testing may cause symptoms, but the smaller amounts of milk or milk products that these persons ingest in their normal diet may not be enough to cause symptoms. Technically, they may be lactose intolerant when they are tested with larger amounts of milk, but lactose in their normal diet cannot be responsible for their usual symptoms.

Recognition of this issue is important in interpreting the results of a milk challenge.