Symptoms and Signs of Lactose Intolerance

Medical Author: John P. Cunha, DO, FACOEP
Medically Reviewed on 3/11/2019

Doctor's Notes on Lactose Intolerance

Lactose intolerance is a common disorder caused by the inability to digest lactose, a carbohydrate found in milk and other dairy products. Normally, lactose is broken up by an enzyme called lactase located on the lining of the intestines that works to break up lactose into its smaller carbohydrate components, glucose and galactose. These two smaller molecules are more easily absorbed by the body and used for metabolism. Most commonly, lactose intolerance is an acquired condition. The intestinal wall can become damaged, commonly from infections or certain medications such as gastroenteritis, celiac disease, Crohn's disease, radiation therapy, diabetic enteropathy, HIV enteropathy, and some chemotherapeutic drugs. The complete absence of lactase at birth is a rare genetic condition where the gene responsible for producing the lactase enzyme is defective.

Symptoms of lactose intolerance include bloating, abdominal pain, diarrhea and loose stools, flatulence (passing gas), and nausea.

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Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.