Lactose intolerance

Lactose intolerance is digestive symptoms caused by insufficient lactase activity in the small intestine, which leaves lactose incompletely digested. It differs from milk allergy, an immune reaction to milk proteins.

Lactase: Lactase is the small-intestinal enzyme that splits lactose into glucose and galactose. Reduced lactase activity is the immediate cause of lactose malabsorption.
Lactase nonpersistence: Lactase nonpersistence is the genetically programmed decline in lactase production after childhood. It is the most common biological basis for adult lactose intolerance worldwide.
Lactose-free diet: A lactose-free diet excludes or limits foods containing lactose. Reducing lactose intake can relieve symptoms, although complete avoidance is not always necessary.
Lactose threshold: A lactose threshold is the amount of lactose a person can consume before experiencing symptoms. Many people with intolerance tolerate some lactose, so the threshold guides practical intake.
Lactose malabsorption: Lactose malabsorption occurs when unabsorbed lactose passes from the small intestine into the colon. It describes the digestive failure that can produce symptoms, though malabsorption does not always cause them.
Lactase persistence: Lactase persistence is continued lactase production into adulthood, allowing digestion of lactose in many people. Its distribution contrasts with the usual age-related decline that can underlie intolerance.
Lactase supplement: A lactase supplement supplies the enzyme in tablets or drops to help digest dietary lactose. Taking lactase with dairy can reduce symptoms for some people.
Lactose in food: Lactose in food varies by product, processing, and serving size. Comparing dairy products helps explain why equivalent servings can provoke different symptoms.
Colonic fermentation: Colonic fermentation is the microbial breakdown of substances in the large intestine, producing gases and other metabolites. Gut microbes ferment unabsorbed lactose, contributing to gas and bloating.
LCT gene: The LCT gene encodes lactase, the enzyme that digests lactose. Regulatory variation near this gene influences whether lactase production continues after childhood.

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