It is estimated that 65% of the world's population is lactose intolerant. Lactose intolerance that goes undiagnosed or ignored can cause severe digestive symptoms that reduce quality of life. Recognizing the signs and symptoms of lactose intolerance assists in accurate diagnosis and effective management through diet and adjunctive therapies.
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What Is Lactose Intolerance?
Lactose is a sugar found in milk and dairy products. It is classified as a disaccharide because it is made from two simpler sugars: glucose and galactose. For lactose to be absorbed into the bloodstream, it must first be broken down into these monosaccharides by the enzyme lactase, which is produced in the small intestine. Lactase hydrolyzes lactose into glucose and galactose. These monosaccharides are then absorbed through the intestinal lining and into the bloodstream.
Lactose malabsorption occurs when the small intestine produces insufficient amounts of lactase. As a result, lactose is not effectively broken down or absorbed and passes into the colon undigested. Lactose malabsorption affects 68% of adults globally.
While lactose malabsorption refers specifically to the impaired digestion and absorption of lactose, lactose intolerance describes the clinical symptoms resulting from this condition. While everyone with lactose intolerance has lactose malabsorption, not everyone with lactose malabsorption is lactose intolerant. (28)
Causes and Risk Factors
A deficiency in the lactase enzyme causes lactose intolerance. There are various reasons why this may occur:
Primary Lactose Intolerance
Also called lactase non-persistence, this is the most common type of lactose intolerance caused by the natural decline in lactase activity. It is prevalent in certain ethnic groups in the United States, including African American, American Indian, Hispanic, and Asian-American populations. Lactase production begins to decline after weaning in infancy, and this condition is observed in up to 70% of the world's population. As a result, it is common for people to gradually become intolerant to lactose-containing foods as they age. (27)
Secondary Lactose Intolerance
Secondary lactose intolerance is caused by injury or illness affecting the small intestine, such as celiac disease, Crohn's disease, gastroenteritis, chemotherapy, or antibiotics. Damage to the intestinal lining impairs the enterocytes' lactase production, causing lactose malabsorption. Depending on the extent of the damage to the small intestine, this condition may be temporary or permanent. (27)
Congenital Lactose Intolerance
Congenital lactose intolerance is a rare, inherited disorder where infants are born with little or no lactase activity due to mutations in the lactase gene. It is inherited in an autosomal recessive pattern, meaning both parents must pass on the gene variant for the child to be affected. This condition is evident from birth; infants cannot digest lactose in breast milk or formula, leading to severe diarrhea and failure to thrive. (27)
Developmental Lactose Intolerance
This transient form of lactose intolerance occurs in premature infants due to the underdeveloped digestive system. Lactase production increases as the infant and its digestive tract mature, resolving the intolerance. (27)
Symptoms of Lactose Intolerance
The symptoms of lactose intolerance typically onset within a few hours of consuming lactose-containing foods and can vary in severity. Undigested lactose draws excess water into the intestines and undergoes fermentation by resident bacteria in the colon (28). The increase of water and gas in the intestines leads to the following gastrointestinal symptoms:
- Abdominal pain
- Bloating
- Gas and flatulence
- Diarrhea
- Nausea
- Vomiting
- Stomach rumbling or growling (called borborygmus)
Diagnosis and Tests
Determining if you are lactose intolerant primarily involves a clinical diagnosis, which can be made through careful patient history and dietary modifications.
How to Know if You're Lactose Intolerant
Digestive symptoms after ingesting lactose-containing foods are highly indicative of lactose intolerance. A diet-symptom diary can be very helpful for patients to keep a detailed record of everything they eat and related symptoms, keeping in mind that lactose intolerance symptoms typically occur within a few hours of eating lactose-containing foods. (25)
Lactose intolerance can be diagnosed with a lactose elimination diet. If symptoms resolve during the elimination phase (typically four weeks) and then return upon reintroduction of lactose, this supports the diagnosis. (25)
Testing Methods
Diagnostic laboratory tests can confirm the clinical diagnosis of lactose intolerance.
Hydrogen Breath Test
The hydrogen breath test is the most commonly utilized test in the clinical setting to diagnose lactose intolerance because it is widely available and accurate. It is positive in 90% of patients with lactose malabsorption. The test involves the patient collecting serial breath samples after consuming 25 to 50 grams of lactose. A rise in breath hydrogen concentrations greater than 20 ppm over baseline is diagnostic for lactose intolerance.
Hydrogen breath tests available to order through Rupa Health include:
- Lactose Malabsorption Breath Test by Commonwealth Diagnostics International, Inc.
- Lactose Intolerance Breath Test by Aerodiagnostics LLC
- trio-smart Malabsorption Breath Test - Lactose by Gemelli Biotech
Lactose Tolerance Test
The lactose tolerance test is generally considered less specific and sensitive than the hydrogen breath test, which may result in more false-positive and false-negative results. It involves administering an oral dose of lactose to the patient and then monitoring digestive symptoms and blood glucose levels. The test is positive if the patient experiences digestive symptoms and an increase in blood glucose levels of less than 20 mg/dL after lactose consumption. (35)
Stool Acidity Test
A stool acidity test measures the pH of a stool sample, which is typically not acidic under normal conditions. In cases of lactose malabsorption, unabsorbed lactose is fermented by colonic bacteria, leading to the production of lactic acid and a decrease in pH (indicating increased acidity). This test is often used in younger children to indicate lactose malabsorption. (20, 37)
Management and Treatment
Dietary manipulation is the primary intervention for addressing lactose intolerance, but research suggests that other effective therapies may also be effective for managing symptoms and improving lactose tolerance.
Dietary Management
A lactose-reduced diet is the preferred nutritional intervention for people with lactose intolerance. Most patients do not require a complete elimination of all lactose-containing foods, and, when possible, it is actually advised to incorporate small amounts of dairy into the diet given that it is a good source of essential nutrients, including calcium, phosphorus, and vitamins A, B2, and D. Research indicates that most people with lactose intolerance can tolerate 12-15 grams of lactose (equivalent to 8-12 oz of milk) daily. (35)
The table below summarizes lactose-containing and lactose-free foods. Patients will tolerate dairy products naturally low in lactose better, whereas high-lactose foods are more likely to cause symptoms and should be avoided or restricted to small quantities.
Ingredients on food labels indicating that a food contains lactose include:
- Milk
- Skim milk
- Lactose
- Whey
- Curds
- Milk by-products
- Milk solids
- Milk powder
Over-the-Counter Solutions
Supplements are available to help improve lactose tolerance and manage digestive symptoms caused by lactose exposure.
Lactase Enzymes
Supplemental lactase digestive enzymes (such as Lactaid or Dairy Ease) can be taken with meals to aid lactose digestion and alleviate gastrointestinal symptoms associated with lactose intolerance. Determining the appropriate dosage of lactase enzymes can be challenging and depends on factors such as the severity of lactase deficiency, the amount of lactose in the diet, and the specific enzyme product used (24, 33). Therefore, lactase enzymes should complement dietary modifications rather than replace them.
Probiotics
Research indicates that probiotic supplements containing lactase-producing bacterial strains, such as Lactobacillus spp., Bifidobacterium longum, and Bifidobacterium animalis, can alleviate gastrointestinal symptoms comparable to lactase enzymes (28). Studies administering probiotic supplements to patients with lactose intolerance at doses of up to 10 billion CFU daily have shown improvements in abdominal pain, bowel sounds, diarrhea, and flatulence. (1, 23)
Symptom Management
Over-the-counter medications and supplements can be taken as needed to manage abdominal pain, gas, and diarrhea.
- Loperamide is used to control acute diarrhea. One small study showed that taking 8 mg of loperamide before consuming lactose was as effective as lactase enzymes in preventing diarrhea and abdominal cramping.
- Simethicone is a medication used to treat flatulence. Activated charcoal is often used as a natural alternative in doses ranging from 140-500 mg three times daily for treating trapped intestinal gas.
- Peppermint oil is an antispasmodic, relaxing the gastrointestinal tract muscles to relieve symptoms of gas and bloating. Enteric-coated capsules are recommended to prevent heartburn and indigestion. Research shows that 182 mg of
When to See a Doctor
Patients should schedule an appointment with a doctor if they have frequent digestive symptoms after eating dairy. A thorough intake, physical exam, and laboratory evaluation will ensure you are given the proper diagnosis and medical treatment.
Consulting with a nutritionist or registered dietician can be helpful in navigating and making sustainable dietary modifications that align with lactose restriction.
Living With Lactose Intolerance
Living with lactose intolerance involves managing symptoms and considering the long-term implications of the condition.
Managing Symptoms
Trigger avoidance, including dairy products and other lactose-containing foods, is extremely effective in managing lactose intolerance symptoms. Patients should read food labels carefully to avoid hidden sources of lactose.
Many non-dairy alternatives using almond, coconut, and soy bases are available to ease the transition to a lactose-free or lactose-restricted diet.
As needed, patients can use over-the-counter medications and supplements to alleviate symptoms of accidental lactose exposure.
Long-Term Outlook
Primary lactose intolerance does not typically resolve. However, secondary lactose intolerance may improve with treatment of the underlying cause. Working with a doctor to diagnose secondary lactose intolerance and treat the underlying health condition increases the likelihood of enhancing lactose tolerance.
Nutritional deficiencies, especially those of calcium and vitamin D, are concerns for patients on long-term dairy-restricted diets. Calcium and vitamin D are important for maintaining bone health; deficiencies can lead to osteoporosis and bone fractures. Ensuring adequate intake of these nutrients involves incorporating calcium- and vitamin D-rich foods into the diet. When this is not possible, dietary supplements should be taken.
- Non-Dairy Dietary Sources of Calcium: bone-in sardines, fortified soymilk, tofu, dark leafy greens, and broccoli (2)
- Non-Dairy Dietary Sources of Vitamin D: liver oil, trout, salmon, UV-exposed mushrooms, and fortified cereals (39)
Additional Information
Interested in learning more? Commonly asked questions about lactose intolerance are answered below:
Lactose Intolerance vs. Milk Allergy
Milk allergy is an immune response triggered by proteins in milk, causing allergic reactions that can range from mild to severe. Milk allergy often appears within the first year of life, while lactose intolerance generally develops later with age.
Symptoms of milk allergy often occur within minutes of exposure and include:
- Hives
- Shortness of breath
- Trouble swallowing
- Swelling of the tongue
- Wheezing
- Nausea and vomiting
- Anaphylaxis
Lactose Intolerance vs. Milk Protein Intolerance
Milk protein intolerance is an immune-mediated adverse reaction to one or more proteins found in milk, such as casein or whey. Symptoms of milk protein intolerance often develop within weeks of introducing milk into a child's diet and include:
- Skin rash
- Eczema
- Abdominal pain
- Vomiting
- Diarrhea
- Wheezing
- Irritability
- Failure to thrive
FAQs
1. What Are Four Common Symptoms of Lactose Intolerance?
The most common symptoms of lactose intolerance are gas, bloating, diarrhea, and abdominal cramps or pain after consuming lactose-containing foods or beverages.
2. How Can I Check If I'm Lactose Intolerant?
Start by keeping a food diary to track symptoms after consuming dairy products. If you eliminate lactose-consuming foods from your diet and symptoms improve, you are likely lactose intolerance. You can ask your doctor for a hydrogen breath test to confirm the diagnosis.
3. Can You Suddenly Become Lactose Intolerant?
Yes, some individuals can develop lactose intolerance suddenly due to illness, injury to the intestines, or certain medical conditions affecting lactase production.
4. What Can Be Mistaken for Lactose Intolerance?
Conditions that can be mistaken for lactose intolerance include:
- Irritable bowel syndrome (IBS)
- Celiac disease
- Inflammatory bowel diseases (such as Crohn's disease or ulcerative colitis)
- Gastroenteritis
- Small intestinal bacterial overgrowth (SIBO)
- Intestinal parasitic infection
- Food allergies
- Food sensitivities
5. How Can I Relieve Lactose Intolerance Pain Immediately?
To relieve lactose intolerance pain immediately, avoid or reduce the intake of high-lactose foods in your diet. You can try lactase enzyme supplements with lactose-containing meals. Research has also revealed good pain-relieving results with taking 182 mg of peppermint oil.
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Summary and Takeaways
- Lactose intolerance manifests primarily with gastrointestinal symptoms such as bloating, abdominal pain or cramps, diarrhea, and excessive gas shortly after consuming lactose-containing foods.
- Individuals can assess their tolerance through self-monitoring with a food diary, trying an elimination diet, or utilizing medical tests like hydrogen breath or lactose tolerance tests ordered by healthcare providers.
- Dietary modifications involve avoiding or reducing lactose intake, opting for lactose-free dairy products or non-dairy alternatives, and using lactase enzyme supplements to aid digestion. These strategies aim to alleviate symptoms effectively, allowing individuals with lactose intolerance to manage their condition and maintain a balanced diet.
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