Lactose intolerance is a digestive disorder in which the body is unable to fully digest lactose, a sugar found in milk and dairy products. This occurs due to a deficiency in the enzyme lactase, which is responsible for breaking down lactose into its simpler sugar components for absorption in the small intestine.
How Lactose Is Normally Digested
Lactase Enzyme Function
- Lactose (a disaccharide) enters the small intestine through dairy consumption.
- The enzyme lactase, produced in the small intestine, breaks lactose into two simpler sugars:
- Glucose (used for energy)
- Galactose (converted into glucose by the liver)
- These sugars are absorbed into the bloodstream for use as energy.
What Happens in Lactose Intolerance?
- Lactase deficiency prevents lactose from being fully broken down.
- Undigested lactose moves into the large intestine (colon).
- Gut bacteria ferment lactose, producing gas, water, and short-chain fatty acids.
- This leads to symptoms such as bloating, diarrhea, and stomach pain.
Types of Lactose Intolerance
Lactose intolerance varies based on the underlying cause of lactase deficiency.
| Type | Cause | Onset | Reversibility |
| Primary Lactose Intolerance | Genetic decrease in lactase production after childhood | Gradual (common in adults) | Permanent |
| Secondary Lactose Intolerance | Damage to the intestinal lining (due to infection, celiac disease, Crohn’s disease) | Sudden (after illness or injury) | Often temporary |
| Congenital Lactose Intolerance | Rare genetic disorder where lactase is absent from birth | Present at birth | Permanent |
| Developmental Lactose Intolerance | Temporary lactase deficiency in premature infants | At birth (premature babies) | Temporary |
Symptoms of Lactose Intolerance
Symptoms typically appear 30 minutes to 2 hours after consuming lactose-containing foods.
Gastrointestinal Symptoms (Most Common)
- Bloating – Excess gas production causes abdominal swelling.
- Diarrhea – Unabsorbed lactose draws water into the colon.
- Abdominal cramps – Fermentation of lactose causes irritation and pain.
- Flatulence (Gas) – Bacterial fermentation produces methane and hydrogen.
- Nausea – Some individuals experience mild nausea after dairy consumption.
Systemic Symptoms (Less Common)
- Fatigue – Some individuals report tiredness after dairy consumption.
- Headaches – Likely due to inflammation or gut irritation.
- Muscle and joint pain – Rare but reported in severe intolerance.
Severity varies based on the level of lactase deficiency and the amount of lactose consumed.
Diagnosis of Lactose Intolerance
Lactose Tolerance Test
- Measures blood glucose levels after consuming lactose.
- Low glucose levels indicate poor lactose digestion.
Hydrogen Breath Test
- Most commonly used test.
- Measures hydrogen levels in breath after lactose ingestion.
- High hydrogen indicates bacterial fermentation of undigested lactose.
Stool Acidity Test (For Infants)
- Checks for lactic acid and undigested sugars in stool.
- Used when breath or blood tests are not feasible.
Elimination Diet
- Avoid dairy for 2-4 weeks and observe symptom improvement.
- Reintroduce lactose-containing foods to confirm intolerance.
Management and Treatment of Lactose Intolerance
Lactose intolerance is not life-threatening but requires dietary adjustments to prevent discomfort.
Dietary Modifications
| Dairy Product | Lactose-Free Alternative |
| Cow’s milk | Lactose-free milk, oat milk, soy milk, almond milk |
| Cheese | Hard cheeses (cheddar, parmesan), plant-based cheese |
| Yogurt | Dairy-free yogurt (coconut, almond, soy) |
| Butter | Vegan butter, olive oil, coconut oil |
| Ice Cream | Coconut milk, almond milk, or oat-based ice creams |
Many lactose-intolerant individuals can tolerate small amounts of dairy, particularly aged cheeses and yogurt, which contain lower lactose levels.
Lactase Enzyme Supplements
- Lactase enzyme tablets (e.g., Lactaid) help digest lactose.
- Taken before consuming dairy to reduce symptoms.
Probiotics and Gut Health
- Probiotic strains like Lactobacillus and Bifidobacterium may aid lactose digestion.
- Fermented foods (kimchi, sauerkraut) improve gut microbiota balance.
Ensuring Nutrient Intake
- Calcium and Vitamin D deficiency is a concern with dairy avoidance.
- Dairy-free calcium sources:
- Leafy greens (kale, bok choy)
- Almonds
- Fortified plant-based milks
- Fish with bones (sardines, salmon)
Difference Between Lactose Intolerance and Milk Allergy
| Feature | Lactose Intolerance | Milk Allergy |
| Cause | Lactase enzyme deficiency | Immune reaction to milk proteins (casein, whey) |
| Symptoms | Digestive discomfort (bloating, diarrhea) | Skin reactions, anaphylaxis, respiratory distress |
| Onset | 30 minutes to 2 hours after eating dairy | Immediate to delayed (minutes to hours) |
| Severity | Mild to moderate | Can be life-threatening |
| Management | Avoid lactose, use lactase supplements | Strict dairy avoidance, carry epinephrine (EpiPen®) |
Lactose intolerance affects digestion, while a milk allergy triggers an immune response.
Conclusion
- Lactose intolerance occurs when the body lacks lactase, preventing proper digestion of lactose.
- Undigested lactose ferments in the colon, causing bloating, diarrhea, and gas.
- It differs from a milk allergy, which is an immune response to milk proteins.
- Management includes lactose-free diets, lactase supplements, and alternative calcium sources.