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Lactose Intolerance

The inability to digest or absorb lactose, a type of sugar found in milk and other dairy products.

PubMed Health Glossary
(Source: NIH - National Cancer Institute)

About Lactose Intolerance

Stomach ache, bloating, "gas" and diarrhea are all typical digestive symptoms that some people have after eating or drinking dairy products. People who have difficulty digesting dairy products may only tolerate small amounts of lactose (a sugar found in milk and other dairy products). This is called lactose intolerance.

But some people who are sensitive to milk might actually have a different problem. It is important to get the diagnosis right before deciding to make major changes to your diet, especially in children, teenagers and people who need more calcium.

Lactose intolerance is not an allergy. This is an important difference. People who have a true milk allergy can react to even a tiny amount of dairy foods or milk. But people who are lactose intolerant can sometimes consume quite a lot of these products without having any major problems... Read more about Lactose Intolerance

What works? Research summarized

Evidence reviews

Do probiotics reduce adult lactose intolerance: a systematic review

PURPOSE: To assess the efficacy of oral probiotics in adults with lactose intolerance through a systematic review of its effects on symptoms and breath hydrogen tests, and whether adding probiotics to nonfermented dairy products decreases lactose intolerance at that meal.

Lactase treated feeds to promote growth and feeding tolerance in preterm infants

Very low birth weight preterm infants are often fed through a tube into a vein (parenterally) as adequate growth and nutrition is important for lung and brain development. Early feeding via the gut (enterally) stimulates motility and digestive activity and is associated with improved growth, but this is not always possible. Lactase is an intestinal enzyme that helps digest milk and is slow to develop in preterm infants after birth. Breast milk contains components that help with lactose digestion. Lactose intolerance is often managed in infants born at term with low‐lactose or lactose‐free formulas, but these do not fulfil the nutrition requirements for preterm infants. Feeding intolerance leaves residual feeds in the stomach prior to the next scheduled feeding and causes abdominal distension, bile stained fluid in the lungs (aspirates), and vomiting. Preparations of lactase could potentially be added to formula or breast milk for preterm infants. There was not a significant effect on weight gain in the one randomized controlled trial identified that investigated addition of lactase. The review authors searched the medical literature thoroughly but found only this one high quality trial enrolling 130 preterm infants. No adverse effects were noted and lactase treated feeds appeared to be well tolerated.

Lactose malabsorption and intolerance: a systematic review on the diagnostic value of gastrointestinal symptoms and self-reported milk intolerance

BACKGROUND: When lactose malabsorption gives rise to symptoms, the result is called 'lactose intolerance'. Although lactose intolerance is often bothersome for patients, once recognized it may be managed by simple dietary adjustments. However, diagnosing lactose intolerance is not straightforward, especially in primary care.

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Summaries for consumers

Living with lactose intolerance

People who have lactose intolerance are still able to eat and drink small amounts of dairy products - preferably together with other foods. So far there is no conclusive proof that lactase products and probiotic nutritional supplements help to digest lactose better. Most people with lactose intolerance have no or almost no symptoms when they ingest small amounts of lactose. Symptoms can also be milder if the dairy products are consumed together with other foods. That is because solid or fatty foods slow down the digestion process in the stomach. Less lactose then enters the intestine in one go, and the intestine reacts less sensitively. Research has indicated that some people can tolerate lactose better if they carefully and gradually increase the amount of lactose in their diet. But this has not been tested enough yet.

Causes and diagnosis of lactose intolerance

Some people have digestive problems after drinking milk or eating dairy products. They may only tolerate very small amounts of lactose because their bowel has trouble breaking it down. Lactose is the main carbohydrate in milk produced by cows and other animals. Human breast milk also contains lactose. It is not present in vegetable products like soy milk. Lactose consists of two sugars: glucose and galactose. An enzyme in our small intestine called lactase quickly breaks down the lactose into its two parts. Only after the two sugars have been separated can they be absorbed by our bowel.

Lactose intolerance: Overview

Stomach ache, bloating, "gas" and diarrhea are all typical digestive symptoms that some people have after eating or drinking dairy products. People who have difficulty digesting dairy products may only tolerate certain amounts of lactose (a sugar found in milk and other dairy products). This is called lactose intolerance.

See all (8)

Terms to know

Diarrhea
Frequent, loose, and watery bowel movements. Common causes include gastrointestinal infections, irritable bowel syndrome, medicines, and malabsorption.
Digestion
The process of breaking down food into substances the body can use for energy, tissue growth, and repair.
Enzymes
Protein made by the body that brings about a chemical reaction - for example, the enzymes produced by the gut to aid digestion.
Intestinal Gas
Gas or air in the gastrointestinal tract.
Lactase
An enzyme in the small intestine needed to digest milk sugar (lactose).
Lactose
A type of sugar found in milk and milk products.
Nausea
A feeling of sickness or discomfort in the stomach that may come with an urge to vomit.

More about Lactose Intolerance

Photo of an adult

Also called: Cow's milk enteropathy, Lactose malabsorption

Other terms to know: See all 7
Diarrhea, Digestion, Enzymes

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