• acute gastroenteritis is a self-limited illness
• however, damage to the brush border of the small intestine mucosa where lactase is present may lead to a secondary lactase deficiency and subsequent inability to digest lactose properly
• partially or minimally digested lactose moves into the colon where it is fermented by enteric bacteria resulting in hydrogen, carbon dioxide, and acids
• these byproducts result in symptoms reported for those with lactase deficiency: cramps, abominal pain and distension, and flatulence
• the increased solute load in the large intestine leads to increased osmotic pressure, causing watery diarrhea
• early refeeding following gastroenteritis is recommended, but many clinicians recommend dairy restricted diets acutely

References

American Academy of Pediatrics PREP Curriculum