Lactose intolerance is one of the world’s most common digestive issues, yet most people don’t fully understand why it happens or how it affects the body. This guide gives you a complete, science-backed overview, so readers don’t need to go anywhere else to understand the condition.
Lactose intolerance occurs when the body can’t fully digest lactose, the natural sugar found in milk and dairy products. Lactose requires an enzyme called lactase for digestion. If lactase levels are low, lactose travels undigested into the large intestine, where bacteria ferment it, creating gas, bloating, and other symptoms.
Key facts:
- It is a digestive issue, not an allergy.
- It is not dangerous, but can be very uncomfortable.
- It affects millions worldwide, with rates differing by ethnicity.
Normally, the small intestine produces enough lactase to break lactose into glucose and galactose, which the body uses for energy.
When this process fails, lactose remains undigested. In the colon, gut bacteria ferment it, producing:
- Gas (hydrogen, methane)
- Water retention
- Rapid movement through the bowel
This leads to symptoms like bloating and diarrhea.
1. Primary Lactose Intolerance
This is the most common form. Lactase naturally declines after childhood—especially in certain populations.
Typical in:
East Asian, African, Middle Eastern, Indigenous American populations.
Less common in:
Northern Europeans (due to a genetic trait known as lactase persistence).
2. Secondary Lactose Intolerance
Caused by temporary intestinal damage from:
- Gastroenteritis
- Untreated celiac disease
- Crohn’s disease
- Chemotherapy
- Infections
Once the intestine heals, tolerance often improves.
3. Congenital Lactase Deficiency
A rare genetic disorder where babies are born with little or no lactase. Requires immediate medical nutrition support.
4. Developmental Lactase Deficiency
Seen in premature infants whose digestive systems are not fully developed. Usually temporary.
Symptoms usually appear within 30–120 minutes of consuming dairy and vary from mild to severe.
Typical signs include:
- Bloating
- Gas and belching
- Abdominal cramps
- Diarrhea
- Rumbling stomach
- Nausea
Not everyone experiences all symptoms, and tolerance levels vary widely.
1. Elimination & Rechallenge
Temporarily remove lactose from the diet for 1–2 weeks, then reintroduce it. If symptoms return, intolerance is likely.
2. Hydrogen Breath Test
A medically supervised test that measures hydrogen in the breath after consuming lactose. A rise indicates malabsorption.
3. Blood Glucose Test
Lactose ingestion should raise blood sugar; if it doesn’t, digestion is impaired.
4. Stool Acidity Test
Mainly used in infants. Undigested lactose causes acidic stool.
5. Genetic Testing
Can identify genes linked to lactase non-persistence.
Seek medical advice if:
- Symptoms are severe
- You suspect milk allergy
- Weight loss is unintentional
- You have symptoms even without dairy
You suspect celiac disease or IBS
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