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What is lactose intolerance?

Roshini C. Rajapaksa, MD
Gastroenterology

Lactose intolerance occurs when the body doesn't produce enough of the enzyme lactase, which helps digest lactose, the main protein found in dairy products. Watch gastroenterologist Roshini Raj, MD, explain this condition and how it's diagnosed.

Lactose intolerance is a condition where the body doesn't have enough of the enzyme (lactase) to break down the sugar commonly found in milk (lactose). Some people can be missing the enzyme entirely, but for many people, they don't have enough of the enzyme to handle a large load of lactose. Also, many people have the ability to increase their supply of lactase by slow, steady exposure to lactose. Many dietary aids for this condition simply add the enzyme into the dairy product. Diarrhea and bloating are the most common side effects of this deficiency.
Samantha Heller, RD
Nutrition & Dietetics
People who are lactose intolerant do not have the enzyme in their gut that helps digest lactose, called lactase. Lactase helps break apart the galactose-glucose molecule so it can be absorbed. If you do not have the enzyme lactase in your gut, eating dairy products may cause cramping or bloating.
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Lawrence S. Friedman, MD
Gastroenterology
Lactose intolerance is difficulty digesting lactose, the primary sugar found in milk. It's been estimated that up to 70% of the world's people are unable to digest lactose, although the problem is minor for most. The difficulty occurs when a person's body does not produce enough of the enzyme lactase, which breaks down milk sugar into simpler forms that can be absorbed into the bloodstream. Lactose intolerance is more prevalent in certain ethnic groups, including Jews, African Americans, Native Americans, and Asians; it is less common in Scandinavians and other ethnic groups that traditionally depended on dairy foods for a major part of their diet.
F. Michael Gloth, III
Geriatric Medicine
Lactose intolerance is more common as we grow older, and it is often accompanied by nausea, bloating, and even diarrhea or vomiting. Lactose intolerance is caused by the lack of an enzyme called lactase, which is needed to break down lactose -- a sugar found in milk -- into a
useable form.
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Sarah Worden
Nutrition & Dietetics
Lactose intolerance, while it can cause discomfort, is not nearly as severe as a milk allergy.  Lactose intolerance is caused by the body having a difficulty digesting milk sugar (lactose) due to lack of the enzyme, lactase.  Symptoms of lactose intolerance are gas, bloating, diarrhea, and upset stomach.
Lactose is a natural sugar found in milk and other dairy products. During digestion, an intestinal enzyme called lactase breaks down lactose into smaller, more easily digested sugars. People who are lactose intolerant produce too little lactase. Common symptoms are bloating, gas and diarrhea. Some people experience nausea and abdominal pain.

Lactose intolerance is the inability or insufficient ability to digest lactose, a sugar found in milk and milk products. Lactose intolerance is caused by a deficiency of the enzyme lactase, which is produced by the cells lining the small intestine. Lactase breaks down lactose into two simpler forms of sugar called glucose and galactose, which are then absorbed into the bloodstream.

Not all people with lactase deficiency have digestive symptoms, but those who do may have lactose intolerance. Most people with lactose intolerance can tolerate some amount of lactose in their diet.

People sometimes confuse lactose intolerance with cow milk allergy. Milk allergy is a reaction by the body's immune system to one or more milk proteins and can be life threatening when just a small amount of milk or milk product is consumed. Milk allergy most commonly appears in the first year of life, while lactose intolerance occurs more often in adulthood.

This answer is based on source information from  the National Institute of Diabetes and Digestive and Kidney Diseases.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.