Lactose Intolerance

Understanding the condition

From: MedlinePlus, National Library of Medicine

Lactose intolerance means that you cannot digest foods with lactose in them. Lactose is the sugar found in milk and foods made with milk. After eating foods with lactose in them, you may feel sick to your stomach. You may also have:

• Gas
• Diarrhea
• Swelling in your stomach

Your doctor may do a blood, breath or stool test to find out if your problems are due to lactose intolerance.

Lactose intolerance is not serious. Eating less food with lactose, or using pills or drops to help you digest lactose usually helps. You may need to take a calcium supplement if you don't get enough of it from your diet, since milk and foods made with milk are the most common source of calcium for most people.

Genetic causes described in the linked summary

From: MedlinePlus Genetics

Congenital lactase deficiency is caused by variants (also called mutations) in the LCT gene. The LCT gene provides instructions for making the lactase enzyme. Variants in the LCT gene that cause congenital lactase deficiency are believed to interfere with the processing and function of lactase, causing affected infants to have a severely impaired ability to digest the lactose in breast milk or formula.

Lactase nonpersistence in adulthood is caused by the gradually decreasing activity (expression) of the LCT gene after infancy, which occurs in most humans. LCT gene expression is controlled by a DNA sequence called a regulatory element, which is located within a nearby gene called MCM6. Some individuals have inherited changes in this element that lead to sustained lactase production in the small intestine and the ability to digest lactose throughout life. People without these changes have a reduced ability to digest lactose as they get older, resulting in the signs and symptoms of lactase nonpersistence.

Inheritance described in the linked summary

From: MedlinePlus Genetics

Congenital lactase deficiency is inherited in an autosomal recessive pattern, which means both copies of the LCT gene in each cell must have a variant to cause the disorder. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition.

The ability to digest lactose into adulthood depends on which variants in the regulatory element within the MCM6 gene individuals have inherited from their parents. The variants that promote continued lactase production are considered autosomal dominant, which means one copy of the altered regulatory element in each cell is sufficient to sustain lactase production. People who have not inherited these variants from either parent are lactase nonpersistent and will have some degree of lactose intolerance.

Understanding terms used in the source

These definitions explain medical words used above. A definition is not evidence that another condition is present, and it does not predict how a symptom will develop. Ask the clinician which terms apply to the actual examination or test result.

Affected

This term applies to a family member who is diagnosed with the same condition as the individual who is the primary focus of investigation (the proband).

Diarrhea

Abnormally increased frequency (usually defined as three or more) loose or watery bowel movements a day.

Which doctor should you see?

The suggested department for discussing Lactose Intolerance is Gastroenterology, with a gastroenterologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which digestive symptoms or nutritional changes matter most?
• What question would an endoscopy, scan or laboratory test answer if one is proposed?
• How should persistent pain, bleeding or difficulty eating be followed up?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Lactose Intolerance. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.