Lactose Intolerance: Types, Symptoms, Diagnosis, and Practical Management

Lactose Intolerance: When Dairy Doesn't Sit Well

Lactose intolerance is the inability to fully digest lactose (milk sugar) due to insufficient lactase enzyme. Undigested lactose ferments in the colon, causing GI symptoms.

Types and Causes

• Primary (adult-onset): Genetically programmed lactase decline after weaning. Prevalence: ~68% globally; highest in East Asian, West African, Arab, Jewish, Greek, Italian descent.
• Secondary: Temporary lactase loss from small intestinal damage—celiac disease, Crohn's, gastroenteritis, SIBO, chemotherapy, antibiotics, GI surgery.
• Congenital (rare): Autosomal recessive; infants lack lactase from birth.
• Developmental: Preterm infants (<34 weeks) have low lactase; improves with maturity.

Symptoms (30 minutes to 2 hours post-dairy)

• Bloating, distension
• Flatulence
• Diarrhea (osmotic)
• Abdominal cramps
• Nausea, sometimes vomiting
• Borborygmi (audible gut sounds)

Severity depends on lactose dose, residual lactase, gut transit, microbiome.

Diagnosis

• Hydrogen breath test: Gold standard. Lactose load → measure H₂ in breath (bacterial fermentation).
• Lactose tolerance test: Blood glucose rise <20 mg/dL after lactose = malabsorption.
• Genetic test: LCT -13910 C>T variant (primary type).
• Trial elimination: 2 weeks lactose-free → symptom resolution supports diagnosis.

Management

• Dietary modification: Most tolerate 12–15g lactose (1 cup milk) spread across meals. Hard cheeses, yogurt, butter are low-lactose.
• Lactase supplements: Take with first bite of dairy (tablets, drops). Dose per lactose grams.
• Lactose-free products: Milk, ice cream, cottage cheese pre-treated with lactase.
• Plant milks: Soy, oat, almond, pea—choose fortified (Ca, D, B12).
• Calcium/vitamin D: Ensure adequacy via diet/supplements if dairy restricted.

When to See a Doctor

Symptoms persist despite management; unexplained weight loss; blood in stool; onset after age 50 (rule out other pathology).