What happens with lactose intolerance

Mechanism, symptoms, and management for lactose intolerance

Lactose intolerance is a prevalent condition characterized by the partial or total inability to digest lactose, a type of sugar found predominantly in milk and other dairy products. This condition arises when the body produces an insufficient amount of the lactase enzyme, or in rare instances, when the enzyme is entirely absent. As a result, individuals with lactose intolerance may experience various digestive complaints when consuming foods containing lactose. Understanding the underlying mechanism, typical symptoms, diagnostic approaches, and available management strategies is essential for effective dietary planning and long-term well-being.

Suffering from lactose intolerance?

The physiological mechanism behind lactose intolerance

To properly digest lactose, the small intestine must produce the lactase enzyme, which is responsible for splitting lactose into its component sugars—glucose and galactose. In individuals with lactose intolerance, a shortage of the lactase enzyme means that lactose passes undigested through the small intestine and reaches the large intestine. Here, intestinal bacteria ferment the undigested lactose, producing gas and drawing in water. This fermentation process can lead to various unpleasant intestinal complaints, which may vary in intensity depending on the degree of lactase deficiency and the amount of lactose consumed.

Lactose intolerance is classified into several types:

• Primary lactose intolerance: The most common form, in which lactase production decreases gradually with age.
• Secondary lactose intolerance: Developing temporarily following an illness or injury that affects the small intestine.
• Congenital lactose intolerance: A rare, genetic form present from birth due to a complete lack of the lactase enzyme.

Common symptoms associated with lactose intolerance

The fermentation of undigested lactose in the colon typically may trigger a range of non-allergic hypersensitivity symptoms. These include:

• Bloating and abdominal distention
• Intestinal cramps and pain
• Flatulence
• Diarrhea
• Nausea and, less commonly, fatigue

Symptom severity and specific complaints may vary widely among individuals, depending on the amount of lactose ingested, the individual’s residual lactase activity, and the composition of gut bacteria. It is important to note that lactose intolerance is not the same as a cow’s milk protein allergy, which is an immune reaction to milk proteins.

Sources of lactose in the diet

Lactose is most commonly found in milk, yogurt, soft cheeses, cream, and ice cream. It can also appear in processed foods and certain medications, often as an undisclosed additive. While many supermarket products are labeled as “lactose-free,” some may nonetheless contain trace amounts of lactose. For guidance on navigating lactose-containing foods, consult our page on lactose intolerance.

Diagnosis and testing

Accurate diagnosis of lactose intolerance is important for effective management. Clinical assessment may involve the following:

• Hydrogen breath test: Measures hydrogen levels in breath after lactose ingestion.
• Lactose tolerance blood test: Assesses glucose levels following lactose consumption.
• Stool acidity test: Used primarily in young children.
• Elimination diet: Temporarily avoids lactose-containing foods to observe symptom changes.

These diagnostic tools help distinguish lactose intolerance from other gastrointestinal conditions. You can also do an online intolerance test (2 minutes), which can give you an indication if you have lactose intolerance.

Managing lactose intolerance effectively

A central component of managing lactose intolerance is adopting a lactose-poor diet tailored to the individual’s tolerance threshold. Many people may be able to tolerate small amounts of lactose without significant complaints, while others require stricter avoidance. Incorporating lactose-free or plant-based dairy alternatives can help maintain nutritional adequacy, particularly for nutrients such as calcium, vitamin B12, and vitamin B2.

In addition to dietary modification, supplements containing the lactase enzyme—such as those available in tablet, capsule, or drop form—may assist with lactose digestion, allowing greater dietary flexibility. Certain probiotic supplements that include lactase-producing strains may also help support digestive comfort.* Explore our lactase range for lactose intolerance to learn about potential supplement options.

Conclusion

Lactose intolerance represents a common, non-allergic hypersensitivity resulting from insufficient lactase enzyme activity in the small intestine. Unpleasant intestinal complaints such as bloating, abdominal pain, and diarrhea may occur after dairy consumption. Accurate diagnosis and a well-structured management plan—including dietary changes, enzyme supplements, and professional support—can help those affected enjoy food confidently and maintain optimal nutrition.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.