Lactose Intolerance: Symptoms, Diagnosis, Diet, Treatment
Medical review pending
This educational article does not replace care from a licensed clinician. Automated publication checks and human medical review are separate states; the review label above reflects the recorded state for this exact content.
Introduction
Lactose intolerance can cause bloating, gas, belly pain, diarrhea, and nausea after eating lactose2,5. Lactose is a natural sugar in milk and other dairy foods1,8.
The condition starts when the small intestine makes too little lactase1,2. Lactase is an enzyme that breaks lactose into sugars the body can absorb6,10.
A clear plan can help reduce pain without banning all dairy foods. Many people with lactose intolerance can still handle some lactose4,9.
This guide covers lactose intolerance symptoms, diagnosis, treatment, and diet choices. It also explains how to protect calcium and vitamin D intake.
Ask with sources
Ask ModernDoc anything about Lactose Intolerance: Symptoms, Diagnosis, Diet, Treatment
Ask a question about Lactose Intolerance: Symptoms, Diagnosis, Diet, Treatment→What should I know about Lactose Intolerance: Symptoms, Diagnosis, Diet, Treatment?Answers open in the ModernDoc app.
ModernDoc provides evidence-based health information with cited sources — not medical advice. If this may be an emergency, call 911.
Overview: What Lactose Intolerance Is
How lactase helps digest lactose
Lactase sits along the inner lining of the small intestine6. It breaks lactose into two simpler sugars called glucose and galactose6,10.
The body can then absorb these smaller sugars6,10. This process usually happens without gas forming in the small intestine10.
Low lactase levels leave some lactose undigested2,5. The lactose then moves from the small intestine into the colon5,10.
Bacteria in the colon break down, or ferment, the lactose5,10. This process creates gas, including hydrogen5,10.
The remaining lactose also pulls water into the colon5,10. The extra gas and water can cause bloating, cramps, and diarrhea5,10.
This process also explains the hydrogen breath test. The test measures hydrogen formed when bacteria break down undigested lactose7,10.
Lactose malabsorption versus lactose intolerance
Lactose malabsorption means the small intestine cannot digest all the lactose a person eats2,8. It occurs when the small intestine makes too little lactase2.
Lactose intolerance means that lactose malabsorption causes digestive symptoms5,8. These symptoms may include gas, bloating, diarrhea, nausea, or belly pain2,5.
Not everyone with lactose malabsorption develops symptoms5,8. A person can have low lactase levels and still digest some dairy foods9.
Many people with lactose intolerance can also tolerate some lactose4,9. The amount that causes symptoms differs from person to person4,5.
Lactose intolerance is not the same as a milk allergy8. Lactose intolerance is a digestive reaction, while a food allergy involves the immune system8.
Causes of Lactose Intolerance
Low lactase production causes lactose malabsorption and related digestive symptoms1,2. Several factors can lead to low levels of this enzyme1,6.
Primary lactose intolerance
Primary lactose intolerance develops when lactase production falls after early childhood1,6. It is common in adults, but the starting age can vary1.
This form does not come from an injury or disease in the small intestine6. Symptoms can start when lactase levels become too low for the lactose eaten9.
People may still digest small amounts of lactose4,9. Their limit may depend on how much lactase their small intestine still makes2,9.
Secondary lactose intolerance
Secondary lactose intolerance can follow an illness or injury in the small intestine6. Damage to the intestinal lining can lower lactase production6,7.
The change may cause short-term or lasting problems with lactose digestion6,7. Treating the underlying condition may improve lactose digestion over time7.
The return of lactase activity can take months in some people7. A clinician can guide food changes during recovery.
Developmental and congenital causes
Babies born early may have temporary lactose intolerance1. Their intestines may not be ready to make enough lactase1.
Full-term children often do not show common lactose intolerance signs before age three1. Symptoms that affect young children should be reviewed by a healthcare professional.
Congenital lactase deficiency is an inherited form present from birth6. In this rare form, lactase is absent or extremely low6.
It differs from the common drop in lactase that occurs later in life6. Children should not begin a restricted diet without medical guidance4.
Symptoms and Typical Timing
Common lactose intolerance symptoms include:
Bloating or swelling in the belly2,5
Belly pain or cramps2,5,10
Diarrhea or loose stools2,5,10
A feeling of fullness in the belly5
These symptoms occur after eating or drinking products that contain lactose2,5. They often start within 30 minutes to two hours5.
However, timing can vary between people5. The symptoms may also differ between one meal and the next4,5.
Why symptom severity differs
The amount of lactose that causes symptoms differs between people4,5. Many people can have a limited amount without discomfort4.
Symptoms can depend on how much lactase the small intestine still makes2,9. More lactase may allow a person to digest a larger serving9.
The food choice can also affect tolerance4,7. Hard cheeses and some yogurts may be easier to digest than milk or ice cream4,7.
Lactose-free milk is another lower-lactose choice4. Even so, each person should test foods based on their own response.
Symptoms that may point to another problem
Lactose intolerance can feel unpleasant, but it is usually harmless9. However, dairy is not the cause of every digestive symptom.
Blood in the stool is not a symptom to manage with lactose restriction alone. The same applies to unexplained weight loss or fever.
Persistent vomiting, dehydration, or severe belly pain also needs medical care. These signs can point to a problem other than lactose intolerance.
Seek medical advice instead of repeating home food tests. A clinician can check for other causes of the symptoms.
Diagnosis of Lactose Intolerance
A clinician may suspect lactose intolerance from symptoms and food patterns2,7. Improvement after reducing dairy may also support the diagnosis7.
The review should focus on when symptoms start. It should also identify foods and serving sizes linked to symptoms.
Medical history and food diary
A clinician may ask about symptoms, eating habits, family history, and medical history2. These details may show whether symptoms tend to follow lactose intake.
A food and symptom diary can organize this information. Record each food, serving size, meal time, and symptom.
Also note when each symptom began. This can show whether the timing fits a possible lactose reaction.
A clinician may suggest a lactose reduction and reintroduction trial7. This involves reducing lactose and then adding it back in small amounts.
Improvement during reduction may support a suspected link7. Symptoms that return after reintroduction may add more useful information7.
This trial cannot rule out every other digestive condition. A clinician should review symptoms that continue or do not follow a clear pattern.
Do not remove dairy for a long time based only on a short trial. Avoiding dairy without replacements can reduce calcium and vitamin D intake2,4.
Hydrogen breath test
A hydrogen breath test can help confirm lactose malabsorption7. The person first drinks a liquid that contains a large amount of lactose7.
Breath samples are then collected at set times7. The test measures how much hydrogen is present in the breath7.
A large rise in hydrogen suggests that lactose was not fully digested7,10. Colon bacteria instead fermented the undigested lactose and made hydrogen7,10.
A healthcare professional should review the result with the person’s symptoms and history2,7. Similar digestive problems can have other causes2,6,10.
Conditions with similar symptoms
Milk allergy differs from lactose intolerance8. A milk allergy involves the immune system, while lactose intolerance involves digestion8.
Irritable bowel syndrome can cause symptoms that resemble lactose intolerance6. Celiac disease and inflammatory bowel disease can also cause similar concerns6.
Other possible causes include infection and small intestinal bacterial overgrowth6,10. Bacterial overgrowth means too many bacteria are present in the small bowel10.
A medical review can help tell these conditions apart. This is important when symptoms are severe, new, or not clearly linked to lactose.
Treatment and Symptom Management
Treatment often starts by lowering lactose enough to control symptoms3,4. Many people do not need to avoid every dairy product4,9.
The best plan protects comfort and nutrition. It should also reflect the person’s own lactose limit.
Finding a personal lactose limit
A low-lactose diet reduces lactose without banning all dairy products3,7. Most people with lactose intolerance can eat at least some lactose4.
Start by tracking foods, portions, and symptoms. Then reduce one likely source instead of changing the whole diet at once.
Small portions may help reveal which foods are tolerated. Test one product at a time so the result is easier to judge.
A person’s limit can vary by food and serving size4,5. A portion tolerated by one person may cause symptoms in another4,5.
Hard cheese may be easier to tolerate than soft cheese or milk4,7. Some yogurt and lactose-free milk may also work well4,7.
Using lactase supplements
Lactase supplements contain the enzyme that breaks down lactose3. They are sold as tablets and drops3.
Lactase tablets are taken before eating or drinking milk products3. Lactase drops can be added to milk before drinking it3.
These products break down some lactose before it reaches the colon3. They can lower the chance of symptoms for some people3.
Results can differ between people. Lactase supplements should be part of careful food testing, not a substitute for diagnosis.
Young children should not use lactase products without medical advice3. Pregnant people should also speak with a healthcare professional first3.
Treating secondary lactose intolerance
Secondary lactose intolerance comes from another small-intestinal disease or injury6,7. Treatment should address both the lactose symptoms and the underlying problem6,7.
Treating that condition may restore some lactose digestion7. This improvement may take several months7.
A clinician can advise when to test lactose again. Reintroduction should match the person’s recovery and symptoms.
A Practical Low-Lactose Diet
A low-lactose diet should not remove more foods than needed. Many people can keep some dairy foods in their meals4,9.
The plan should also protect calcium and vitamin D intake2,4. A dietitian can help when food choices become too limited4.
Foods that may contain more lactose
Milk and other dairy products are the main sources of lactose1,4. Products that may contain meaningful amounts include:
Cow’s milk and drinks made with milk4
Cream and foods made with cream7
Dry milk powder or milk solids4
Foods made with whey, milk, or lactose4
Serving size matters when testing tolerance. Record both the food and the amount eaten.
A large glass of milk may cause more trouble than a small serving. Individual responses still vary, so personal testing remains important4,5.
Lower-lactose choices
Hard cheeses often contain less lactose and may be easier to tolerate4,7. Some yogurts may also cause fewer symptoms for some people4.
Lactose-free milk has had its lactose reduced or broken down4. It allows many people to keep milk in their diet while lowering lactose intake4.
These foods may be better tolerated than regular milk or ice cream4,7. However, no single food works for everyone.
Add one product at a time. Write down the amount eaten and any symptoms that follow.
Reading labels for hidden lactose
Lactose can appear in prepared foods that do not seem dairy-based4. Reading ingredient lists can help find these sources.
Prepared foods may contain milk ingredients4. Labels can differ between brands, so check each product.
Keep portion size in mind. A small amount of a milk ingredient may be tolerated by some people4,5.
Calcium, vitamin D, and protein
Avoiding all dairy can lower calcium and vitamin D intake2,4. Suitable replacements are important when dairy foods are limited.
Fortified foods have vitamins or minerals added during production. Nutrition labels show whether a product contains calcium or vitamin D.
A clinician or dietitian can suggest foods that meet these needs4. They can also discuss supplements when food intake may not be enough4.
This support is useful for people who avoid several food groups. It can reduce the risk of making the diet too strict.
Daily Planning
A planned approach can make food testing easier. It may also prevent broad restrictions after one uncomfortable meal.
Step-by-step food testing
Use this process with professional guidance when needed:
1Record usual foods, serving sizes, meal times, and symptoms.
2Mark foods that contain milk or lactose.
3Reduce one likely source at a time.
4Note whether symptoms improve.
5Add back a small portion of one food.
6Record the timing and type of symptoms.
7Increase the portion only when it is tolerated.
Adding back small amounts can help find a personal lactose limit. This approach may preserve food choice because many people tolerate some lactose4,5.
Stop the home trial and seek care if severe or unusual symptoms occur. Do not use restriction alone for blood, fever, weight loss, vomiting, or dehydration.
Building meals
Choose foods based on what you tolerate. Do not assume every dairy product will cause symptoms4,9.
Hard cheese, some yogurt, and lactose-free milk may be useful choices4,7. Lactase supplements may also help with meals that contain lactose3.
A balanced plan should still provide enough calcium and vitamin D2,4. Seek help if your food choices become very limited.
Guidance for Children, Pregnancy, and Restrictive Diets
Children need a dietary plan from a doctor or dietitian4. Removing dairy without replacements can lower calcium and vitamin D intake2,4.
Pregnant people should ask a healthcare professional before using lactase products3. Professional advice is also useful when several food limits overlap.
A dietitian can suggest fortified foods and review nutrient intake4. This may control symptoms without removing more foods than needed.
When to See a Doctor
Contact a healthcare professional if symptoms continue after reducing lactose. Seek advice if symptoms start suddenly or lack a clear link to lactose.
Blood in the stool needs medical review. So do unexplained weight loss, fever, ongoing vomiting, dehydration, or severe belly pain.
These warning signs should not be managed through a self-directed low-lactose diet alone. A clinician can check for causes that need different care.
The clinician may review symptoms, food habits, family history, and medical history2. A hydrogen breath test may help confirm lactose malabsorption7.
Testing may also find another digestive condition6,10. Possible causes include celiac disease, inflammatory bowel disease, infection, or bacterial overgrowth6,10.
Treating an underlying intestinal condition may improve secondary lactose intolerance7. A clinician can guide diet changes while the intestine heals.
Conclusion
Understanding lactose intolerance symptoms, diagnosis, treatment, and diet choices can reduce discomfort. The condition starts when low lactase levels cause lactose malabsorption1,2.
Not everyone with lactose malabsorption has symptoms5,8. Many people with lactose intolerance can still tolerate some lactose4,9.
A personal limit can help keep the diet varied. Hard cheese, lactose-free milk, and some yogurts may be easier to tolerate4,7.
Lactase tablets or drops can also reduce symptoms for some people3. Secondary lactose intolerance may improve when the underlying intestinal condition is treated7.
Avoiding all dairy without replacements can reduce calcium and vitamin D intake2,4. A clinician or dietitian can help protect nutrition while managing symptoms2,4.
Evidence used in this article
- 1. Lactose intolerance: MedlinePlus Medical Encyclopedia
Lactose intolerance: MedlinePlus Medical Encyclopedia Skip navigation
URL of this page: //medlineplus.gov/ency/article/000276.htm
# Lactose intolerance
Lactose is a type of sugar found in milk and other dairy products. An enzyme called lactase is needed by the body to digest lactose.
Lactose intolerance develops when the small intestine does not make enough of this enzyme.
## Causes
Babies' bodies make the lactase enzyme so they can digest milk, including breast milk.
- Babies born too ea
- 2. Lactose Intolerance - NIDDK
Lactose Intolerance - NIDDK
1. Home
2. Health Information
3. Digestive Diseases
4. Lactose Intolerance
English
Related Topics
# Lactose Intolerance
View or Print All Sections
## Definition & Facts
If you have lactose intolerance, you have digestive symptoms—such as bloating, diarrhea, and gas—after you consume foods or drinks that contain lactose. Lactose intolerance may affect your health if it keeps you from getting enough nutrients, such as calcium and vitamin D.
## Symptoms & Causes
- 3. Treatment for Lactose Intolerance - NIDDK
Treatment for Lactose Intolerance - NIDDK
Related Topics
English
# Treatment for Lactose Intolerance
## How can I manage my lactose intolerance symptoms?
In most cases, you can manage the symptoms of lactose intolerance by changing your diet to limit or avoid foods and drinks that contain lactose, such as milk and milk products.
Some people may only need to limit the amount of lactose they eat or drink, while others may need to avoid lactose altogether. Using lactase products can help some
- 4. Eating, Diet, & Nutrition for Lactose Intolerance - NIDDK
Eating, Diet, & Nutrition for Lactose Intolerance - NIDDK
1. Home
2. Health Information
3. Digestive Diseases
4. Lactose Intolerance
5. Eating, Diet, & Nutrition
Related Topics
English
# Eating, Diet, & Nutrition for Lactose Intolerance
## How should I change my diet if I have lactose intolerance?
Talk with your doctor or a dietitian about changing your diet to manage lactose intolerance symptoms while making sure you get enough nutrients. If your child has lactose intolerance, help your c
- 5. What I need to know about Lactose Intolerance
Lactose intolerance means you have symptoms
such as bloating, diarrhea, and gas after you have
milk or milk products.
If your small intestine does not produce much
lactase, you cannot break down much lactose.
Lactose that does not break down goes to your
colon. The colon is an organ that absorbs water
from stool and changes it from a liquid to a solid
form. In your colon, bacteria that normally live in
the colon break down the lactose and create fluid
and gas, causing you to have sympt
- 6. Lactose Intolerance - StatPearls - NCBI Bookshelf
Lactose intolerance is a clinical syndrome characterized by gastrointestinal symptoms following the ingestion of lactose-containing foods. In healthy individuals, dietary lactose is hydrolyzed into glucose and galactose by lactase, an enzyme located in the brush border of the small intestine. Deficiency of this enzyme, whether from primary genetic factors or secondary to intestinal injury, results in incomplete lactose digestion, leading to fermentation by colonic bacteria and the development of
- 7. Lactose intolerance - Diagnosis & treatment
Lactose intolerance - Diagnosis & treatment - Mayo Clinic
## On this page
Diagnosis
Treatment
Self care
Alternative medicine
Preparing for your appointment
---
## Diagnosis
A healthcare professional might suspect lactose intolerance based on someone's symptoms and response to reducing the amount of dairy foods in the diet.
A diagnosis can be confirmed by doing a hydrogen breath test. This test involves drinking a liquid that contains high levels of lactose. The amount of hydrogen in yo
- 8. Lactose Intolerance: Symptoms, Diagnostic Tests & Treatment
Lactose Intolerance: Symptoms, Diagnostic Tests & Treatment
...
Lactose intolerance occurs in people who lack the enzyme they need to break down lactose, the sugar in milk. It causes digestive distress when you eat dairy products. A food intolerance is different from a food allergy.
...
Lactose intolerance is a reaction in your digestive system to lactose, the sugar in milk. It causes uncomfortable symptoms after you eat dairy products. Many people have difficulty digesting lactose, but not ever
- 9. Lactose intolerance - Symptoms & causes - Mayo Clinic
Lactose intolerance - Symptoms & causes - Mayo Clinic
## On this page
Overview
Symptoms
When to see a doctor
Causes
Risk factors
---
## Overview
Lactose intolerance is a condition that makes it hard to digest the sugar in milk and milk products, called lactose. People with lactose intolerance often have diarrhea, gas and bloating after eating or drinking foods containing lactose. The condition is usually harmless, but its symptoms can cause discomfort.
Too little of an enzyme made in t
- 10. Lactose Intolerance
## What is lactose intolerance?
...
Lactose intolerance is a common cause of abdominal cramping, bloating, and loose stools. This condition occurs when the body does not have enough of the intestinal enzyme lactase. The job of lactase is to break down lactose, the main sugar in milk. Once lactose is broken down into simpler forms of sugar, these simple sugars can be absorbed into the bloodstream.
...
In normal digestion, lactose is digested in the small intestine without the release of gas bubbl
Keep the evidence
Take Lactose Intolerance: Symptoms, Diagnosis, Diet, Treatment questions with you.
- Every answer cited to a checkable source
- Sources graded by evidence tier
- Your questions and their evidence, kept
Scan to open the download page