Lactose Intolerance

Lactose intolerance is a common digestive condition in which the body cannot properly digest lactose, the sugar found in milk and various dairy products. It happens due to a deficiency in the lactase enzyme, produced in the small intestine. This inability leads to a range of uncomfortable symptoms, such as bloating, diarrhoea, gas, and nausea.

These symptoms typically occur after consuming lactose-containing foods or drinks and can include abdominal pain. Understanding the causes and symptoms of lactose intolerance is crucial for those affected by this condition. This knowledge helps individuals manage their condition effectively and maintain a healthy, comfortable lifestyle.

What is Lactose Intolerance?

Lactose intolerance is a digestive disorder that should not be confused with a milk allergy, which is an immune system reaction to milk proteins. It specifically refers to the digestive issues that arise when the small intestine does not produce sufficient lactase. This condition can affect individuals of all ages, from infants to adults. It is more common in certain ethnic groups, such as African Americans, Asian Americans, Hispanics/Latinos, and Native Americans. 

The severity of lactose intolerance can vary from person to person. Some individuals may tolerate small amounts of lactose without experiencing significant symptoms. In contrast, others may need to avoid lactose-containing products entirely to prevent discomfort.

There are four main types of lactose intolerance, each with distinct causes.

• Primary Lactose Intolerance: The most prevalent form of lactose intolerance, it typically develops after infancy and may begin in childhood, adolescence, or adulthood (Goosenberg & Afzal, 2025). The body naturally reduces lactase enzyme production in the small intestine. This condition is more prevalent among people of African, Asian, Hispanic, and American Indian descent.
• Secondary Lactose Intolerance: In secondary lactose intolerance, the small intestine reduces lactase production. The decrease can occur due to an illness, injury, or surgery affecting the small intestine. Additionally, bacterial overgrowth and Crohn's disease are linked to secondary lactose intolerance.
• Congenital Lactose Intolerance: Congenital lactose intolerance is a rare form of lactose intolerance. Babies are born with a complete deficiency of the lactase enzyme due to a genetic disorder. This condition can be life-threatening if not promptly recognised and treated.
• Developmental Lactose Intolerance: Developmental lactose intolerance affects premature babies specifically. This condition usually improves as the baby's small intestine matures. Most infants outgrow this type of lactose intolerance with time.

Early signs of lactose intolerance can manifest in various ways but typically involve gastrointestinal discomfort after consuming dairy products. Some key early signs include:

• Flatulence: Excessive gas production can be an early indicator of lactose intolerance, especially if it occurs consistently after consuming milk or dairy products.
• Abdominal Discomfort: Mild abdominal pain, bloating, or a feeling of fullness after consuming lactose-containing foods may be an early sign of intolerance.
• Loose Stools: While not as severe as full-blown diarrhoea, having looser or more frequent stools after consuming dairy can be an early indication of lactose intolerance.
• Nausea: Some individuals may experience mild nausea after consuming lactose, even before other symptoms appear.

Lactose intolerance is the inability to digest lactose due to insufficient lactase enzyme production in the small intestine. Common symptoms of lactose intolerance include:

• Diarrhoea: This is one of the most common symptoms of lactose intolerance and typically occurs within 30 minutes to 2 hours after lactose ingestion.
• Bloating and Gas: Undigested lactose can lead to bloating and excessive gas production in the intestines.
• Abdominal Cramps: Pain and discomfort in the abdomen can result from lactose fermentation by bacteria in the colon.
• Nausea and Vomiting: Some people with lactose intolerance may feel nauseous and vomit after consuming dairy products.

Lactose intolerance happens when the body can't digest lactose, the sugar in dairy products. The leading causes include:

• Lactase Deficiency: The body produces insufficient lactase, which prevents proper digestion of lactose in the small intestine.
• Genetic Factors: Congenital lactose intolerance is caused by variants of the LCT gene (which gives instructions to form the lactase enzyme). (Lactose Intolerance: MedlinePlus Genetics, n.d.)
• Intestinal Damage: Secondary lactose intolerance results from damage to the small intestine caused by infections, diseases, or surgeries.
• Premature Birth: Premature infants may experience temporary lactose intolerance due to their underdeveloped small intestines. (Goosenberg & Afzal, 2025)

Several factors can increase the risk of developing lactose intolerance, including genetic, developmental, and medical conditions.

• Ethnic Background: Individuals from African, Asian, Hispanic, Mediterranean, and Southern European backgrounds have a higher genetic risk of developing lactose intolerance.
• Intestinal Diseases: Conditions such as celiac disease or Crohn's disease can increase the risk of secondary lactose intolerance by damaging the intestines.
• Bowel Damage: Bowel infections or surgeries can cause damage to the small intestine, leading to lactose intolerance.

Diagnosing lactose intolerance involves a combination of symptom assessment and medical tests to confirm the condition. A doctor typically begins with a detailed medical history and a physical examination to evaluate symptoms such as bloating, diarrhoea, and abdominal pain after consuming dairy. If lactose intolerance is suspected, several diagnostic tests can be performed to confirm the diagnosis:

1. Lactose Breath Test

The lactose breath test is one of the most commonly used, non-invasive methods for diagnosing lactose intolerance. During this test:

• The patient consumes a liquid containing a specific amount of lactose.
• Over the next few hours, the patient breathes into a specialised bag at regular intervals.
• The collected breath samples are analysed for hydrogen levels.
• If the body cannot digest lactose properly, it ferments in the colon, producing excess hydrogen, which is released into the breath. A high level of hydrogen in the breath confirms lactose intolerance.

2. Lactose Tolerance Test

The lactose tolerance test measures how the body processes lactose by monitoring blood sugar levels. The process involves:

• The patient consuming a liquid containing lactose.
• Blood samples are taken at different intervals to measure glucose levels.
• If the body properly digests lactose, blood glucose levels should rise.
• A minimal increase in blood glucose indicates that the body is not effectively absorbing lactose, confirming lactose intolerance.

3. Milk Tolerance Test

This test works similarly to the lactose tolerance test but uses regular milk instead of pure lactose. The process includes:

• The patient consuming 500ml of milk.
• Blood sugar levels are measured before and after consumption.
• A rise in blood sugar of less than 9 mg/dL indicates lactose intolerance, as it suggests poor lactose absorption into the bloodstream.

4. Stool Acidity Test

The stool acidity test is primarily used for diagnosing lactose intolerance in infants and young children. The test works as follows:

• A stool sample is collected after lactose is consumed.
• The stool’s acidity is measured because undigested lactose ferments in the colon, producing lactic acid and other fatty acids.
• If the stool is found to be more acidic than normal, it suggests the presence of undigested lactose, confirming lactose intolerance.

5. Small Intestine Biopsy

In rare cases, if other tests are inconclusive or there is suspicion of an underlying digestive disorder, a small intestine biopsy may be performed. The procedure includes:

• A thin, flexible tube (endoscope) is inserted into the intestine via the mouth.
• A small tissue sample is taken from the lining of the small intestine.
• The sample is analysed to measure lactase enzyme activity.
• Low lactase activity confirms lactose intolerance.

The primary approach to managing lactose intolerance is dietary modification to reduce or eliminate lactose intake. The following strategies can help you manage symptoms effectively:

1. Use Lactase Enzyme Supplements

Lactase enzyme supplements, available in tablet or liquid form, can be taken before consuming dairy products. These supplements help break down lactose, allowing individuals to consume dairy without experiencing symptoms. This option is handy when dining out or occasionally consuming dairy-based foods.

2. Probiotics for Lactose Digestion

Probiotics contain beneficial bacteria that may help improve symptoms in some individuals, but evidence remains limited and variable. Some probiotic strains, such as Lactobacillus acidophilus and Bifidobacterium, produce lactase, helping break down lactose more efficiently. Regular consumption of probiotic-rich foods like yoghurt, kefir, and fermented foods may help reduce symptoms over time.

 3. Limit Lactose Intake

People with lactose intolerance should reduce their consumption of high-lactose foods such as milk, cheese, butter, and ice cream. Instead, they can opt for low-lactose or lactose-free dairy products to avoid discomfort while maintaining a balanced diet.

4. Choose Lactose-Free Alternatives

Many grocery stores offer lactose-free options such as lactose-free milk, yoghurt, and cheese. These products contain lactase enzyme, which helps break down lactose, making them easier to digest. Non-dairy alternatives like almond milk, soy milk, and coconut milk are also excellent choices.

5. Gradually Introduce Lactose

Some individuals can tolerate small amounts of lactose without severe symptoms. Gradually reintroducing lactose-containing foods in controlled portions can help determine an individual's tolerance level. Consuming lactose with other foods may also help reduce symptoms.

6. Read Food Labels Carefully

Lactose can be hidden in many processed foods, including baked goods, sauces, soups, and processed meats. Reading ingredient labels carefully helps identify lactose-containing ingredients such as milk, whey, curds, and milk by-products.

Ensure adequate intake of calcium and vitamin D when reducing dairy consumption to prevent nutritional deficiencies

While lactose intolerance is generally not a serious condition, there are certain situations in which it is important to seek medical attention. If you experience severe or persistent symptoms of lactose intolerance, such as abdominal pain, bloating, diarrhoea, or nausea, it is advisable to consult a doctor. These symptoms may indicate a more serious underlying condition, such as celiac disease or inflammatory bowel disease.

In addition, if you suspect that an infant or newborn may have lactose intolerance, it is crucial to seek medical advice. Lactose intolerance in newborns and infants is rare. Symptoms such as diarrhoea, vomiting, and failure to thrive may indicate other health issues requiring prompt medical attention.

Your doctor can help diagnose lactose intolerance through various tests, such as the hydrogen breath or lactose tolerance tests. Once diagnosed, your doctor can provide guidance on managing your condition effectively. This includes dietary recommendations and medication options to help you maintain a healthy, symptom-free lifestyle.