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For further information see CMDT Part 15-27: Malabsorption

Key Features

  • Partial to complete lactose intolerance affects ~50 million people in the United States

  • Occurs in 90% of Asian Americans, 70% of African Americans, 95% of Native Americans, 50% of Mexican Americans, 60% of Jewish Americans, < 25% of White adults

  • Also occurs secondary to Crohn disease, celiac disease, viral gastroenteritis, giardiasis, short bowel syndrome, malnutrition

Clinical Findings

  • Bloating, abdominal cramps, and flatulence with mild to moderate amounts of lactose malabsorption

  • Diarrhea

  • Differential diagnosis

    • Inflammatory bowel disease

    • Mucosal malabsorptive disorders

    • Irritable bowel syndrome

    • Pancreatic insufficiency


  • Diarrheal stool specimens have an increased osmotic gap and pH < 6.0

  • Hydrogen breath test: After ingestion of 50 g lactose, a rise in breath hydrogen of > 20 ppm within 90 minutes is a positive test

  • Empiric trial of a lactose-free diet for 2 weeks leads to resolution of symptoms


  • Eliminate or restrict milk products

  • Spread dairy product intake throughout the day

  • Use lactase enzyme supplements (eg, nonprescription formulation [LactAid]) when ingesting dairy products

  • Calcium supplementation: calcium carbonate 500 mg orally two to three times daily

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