When is lactose contraindicated?

When is Lactose Contraindicated?

Lactose is absolutely contraindicated in classic galactosemia, and should be temporarily avoided in patients with confirmed lactose intolerance causing symptoms, particularly during acute diarrheal illness in infants and during chemotherapy-induced diarrhea in adults. 1, 2

Absolute Contraindications

Classic Galactosemia

• Classic galactosemia (GALT enzyme deficiency) is the only absolute contraindication to lactose ingestion. 1, 2, 3
• This autosomal recessive disorder presents in the neonatal period with jaundice, hepatosplenomegaly, hepatocellular insufficiency, food intolerance, hypoglycemia, renal tubular dysfunction, muscle hypotonia, sepsis, and cataracts after galactose ingestion. 2
• All galactose must be removed from the diet immediately when diagnosis is suspected, with lifelong lactose restriction required even though long-term complications (mental retardation, verbal dyspraxia, motor abnormalities, hypergonadotrophic hypogonadism) still occur despite strict dietary adherence. 2, 3
• Diagnosis is confirmed by measuring GALT enzyme activity in erythrocytes. 2

Relative Contraindications (Temporary Avoidance)

Acute Diarrhea in Infants and Children

• For bottle-fed infants with acute diarrhea, lactose-free or lactose-reduced formulas should be used immediately upon rehydration. 1
• When lactose-free formulas are unavailable, full-strength lactose-containing formulas can be used under close supervision to monitor for carbohydrate malabsorption complications. 1
• True lactose intolerance during acute diarrhea is diagnosed by exacerbation of diarrhea when lactose-containing formula is introduced, not merely by the presence of low stool pH (<6.0) or reducing substances (>0.5%) without clinical symptoms. 1
• Breast-fed infants should continue nursing on demand even during acute diarrhea. 1

Chemotherapy-Induced Diarrhea

• In adult cancer patients with diarrhea during chemotherapy, avoidance of milk and dairy products (except yogurt and firm cheeses) is a reasonable strategy to reduce symptom intensity and duration. 1
• Bowel mucosal injury from chemotherapy may lead to secondary lactose intolerance with abdominal pain, flatulence, diarrhea, and poor nutritional status. 1
• Hypolactasia frequency significantly increases during adjuvant 5-FU-based chemotherapy but is fully reversible after therapy discontinuation. 1
• There is insufficient evidence for lactose-free diet in radiation therapy-induced diarrhea or palliative settings unless clear lactose intolerance is diagnosed. 1

Secondary Lactose Intolerance

• Temporary lactose reduction or removal is appropriate when lactose intolerance is confirmed in the setting of small bowel disease. 1, 4
• Secondary causes requiring temporary lactose avoidance include: celiac disease, gastroenteritis, non-steroidal anti-inflammatory drug use, and other conditions affecting small bowel mucosal integrity. 1, 4
• Lactose intolerance from these secondary causes is generally reversible once the underlying condition is treated. 4

Important Clinical Caveats

Lactose Maldigestion vs. Intolerance

• Lactose maldigestion (inability to digest lactose) does not automatically mean lactose must be avoided—only symptomatic lactose intolerance requires dietary modification. 1, 5, 6
• Most non-Caucasian populations (79% of Native Americans, 75% of African Americans, 51% of Hispanics) have lactose maldigestion after age two, which should be regarded as physiologically normal. 1, 5
• A positive lactose breath test (>20 ppm hydrogen rise) does not reliably predict inability to consume moderate amounts of milk without symptoms. 1, 5
• Many individuals with lactose maldigestion can tolerate moderate quantities of dairy, particularly yogurt and hard cheeses. 1, 4

Diagnostic Considerations

• The hydrogen breath test has a false-negative rate up to 25%, so a negative test does not exclude lactose intolerance—a trial of lactose-free diet should still be considered if symptoms are suggestive. 1, 4
• Testing should be reserved for patients consuming more than 280 ml (0.5 pints) of milk or dairy equivalent daily, as those consuming less can generally tolerate this amount even if lactose intolerant. 4
• Patient self-reports of lactose intolerance correlate poorly with objective evidence and cannot be relied upon for diagnosis. 4

Lactose as Pharmaceutical Excipient

• Lactose-containing medications rarely need to be avoided, as most people with lactose malabsorption can tolerate lactose amounts <12g, and medications contain minimal quantities. 1
• Caution is advised against de-prescribing lactose-containing drugs in cancer patients with diarrhea, as symptoms are more likely from other causes. 1