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Symptoms & causes of lactose intolerance - how can the enzyme lactase help?

People with lactose intolerance cannot tolerate many dairy products. Because they lack an enzyme that is required for the utilization of lactose. The most common symptoms of lactose intolerance are bloating, abdominal cramps and diarrhea. However, lactose intolerance can also make itself felt outside of the gastrointestinal tract. Read here what triggers lactose intolerance, how you can recognize food intolerance and what you can do about the symptoms.

Lactose intolerance: a brief overview

  • Causes: Lack of the enzyme lactase, bacteria produce gases and acids in the large intestine
  • Symptoms: abdominal pain , diarrhea , bloating, intestinal wind, feeling of fullness, nausea, non-specific symptoms such as headaches
  • Diagnostics: H2 breath test , diet/exposure test, symptoms alone provide insufficient information
  • Treatment: Diet adjustments, no dairy products, lactase tablets
  • Prognosis: not a disease, not dangerous, but reduces quality of life

Lactose intolerance: causes and triggers

Dairy products contain milk sugar, also known as lactose. Lactose itself cannot be absorbed by the intestinal mucosa, only the individual sugars that make it up. This means that the milk sugar must first be broken down with the help of an enzyme so that it can pass through the intestinal mucosa into the blood can reach. The enzyme is called lactase. It is normally made by the mucous cells in the small intestine produced - but not or not to a sufficient extent in people with lactose intolerance.

The result: the lactose migrates unchanged from the small intestine to the large intestine. There it serves as food for bacteria. Waste products remain, which then trigger the typical symptoms. These wastes include lactic acids, short-chain fatty acids, and gases such as hydrogen, carbon dioxide, and methane.

Mechanism of lactose intolerance
The effect of lactose in the body - with and without lactase supply in the small and large intestine
In people with lactose intolerance, little or no lactase is produced. The result: the lactose can no longer be broken down and ends up in the large intestine. There certain bacteria ferment the lactose.

Although the reason for lactose intolerance is always a deficiency of the enzyme lactase, this deficiency can occur in different ways. Accordingly, the symptoms vary in severity and can appear for the first time at different ages.


Actually, lactose intolerance is not a disease. Globally, adults who can digest lactose are actually the exception. It's different with babies. Newborns can normally metabolize lactose without any problems. Because they too breast milk contains lactose, even more than cow's milk. But already after the first months of life, the amount of the enzyme gradually decreases.

If it falls below a certain value, lactose intolerance symptoms appear. When that point is reached varies. Therefore, the age at which the so-called primary lactose intolerance begins also varies. Those affected are usually between five and twenty years old. Lactose intolerance is rare in children under the age of five. The first symptoms usually appear in adolescence. Primary lactose intolerance is by far the most common form of milk sugar intolerance.

Incidentally, enzyme production does not stop completely. Most sufferers still have a small amount of the enzyme. There are large individual fluctuations, which is why some people with lactose intolerance can still tolerate a certain amount of lactose in their food, while others react to even the smallest amounts with symptoms.

Thanks to a genetic mutation, about a third of humanity can digest lactose throughout life. Scientists believe that this change in DNA originated in central Europe around 7,500 years ago. In these people, the amount of lactase also decreases, but remains high enough to continue breaking down lactose.

This condition could have been a survival advantage at the time. Because with the beginning of cattle breeding, milk was available in large quantities and became an important source of food. Even today, every person who does not have lactose intolerance is a carrier of this gene mutation.


In contrast to primary lactose intolerance, secondary lactose intolerance is the result of another disease. The production of lactase is not throttled naturally, but by damage to the intestinal mucosa. Triggers are sometimes major operations in the gastrointestinal tract, autoimmune diseases such as Crohn's disease or severe gradients Stomach Flu . Gluten intolerance ( celiac disease ) is often the cause of secondary lactose intolerance, because the intestinal mucosa becomes inflamed with this disease and the production of the enzyme lactase is impaired.

Secondary lactose intolerance usually goes away as soon as the mucosal cells in the Colon have recovered. In rare cases, however, it can become chronic. Ultimately, it always depends on the severity of the disease that caused it.


Congenital lactose intolerance is a very rare form of the disease. Due to a genetic defect, her body can either not produce any lactase at all from the beginning of her life, or only in tiny amounts. It is therefore also referred to as absolute lactose intolerance. The affected babies get persistent diarrhea through breast milk after just a few days. breastfeeding is then not possible. Under certain circumstances, the unsplit lactose can even get directly into the bloodstream via the stomach and intestinal mucosa and cause severe symptoms of poisoning there. The only therapy that can be considered is a lifelong renunciation of lactose.

If newborns have problems with milk sugar, it does not necessarily have to be due to congenital lactose intolerance. The digestive tract can generally react very sensitively in the first few weeks of life. Sometimes the lactase production is not yet running properly, but this problem usually goes away soon.

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Some specialist journals discuss whether an incorrect colonization of the small intestine with bacteria can lead to lactose intolerance. Normally, bacteria and other microorganisms are mainly found in the large intestine. This is completely normal and even very important for them digestion . Under certain circumstances, however, increased colonization of the small intestine can occur, which is problematic.

On the one hand, the incorrect colonization can impair the mucous membrane of the small intestine - and thus the lactase production - and on the other hand the bacteria in the small intestine begin to break down the lactose before it can be broken down by the lactase. There are still no clear research results that confirm this assumption. However, some studies show that in some cases, lactose intolerance disappears once the small intestinal overgrowth is treated with antibiotics.

Lactose intolerance: symptoms

The following symptoms typically occur with lactose intolerance:

  • bloated belly
  • bloating
  • intestinal wind
  • loud bowel sounds
  • stomach pain
  • Nausea, rarely with vomiting
  • Diarrhea

The gas and abdominal pain is caused by the gases produced by bacteria in the colon as they break down lactose. Other waste products that are formed in the process, namely milk and fatty acids, have a "water-pulling" effect. As a result, more fluid flows into the intestine and causes diarrhea.

The symptoms are often made worse by the fact that those affected are embarrassed by the sometimes foul-smelling intestinal gas, which is why they understandably withhold them in public. If the air cannot escape, the intestines continue to expand and the abdominal pain increases.

Paradoxically, lactose intolerance can also increase constipation to lead. This is when methane is mainly produced during the decomposition of lactose. This gas slows down the movement of the bowel, causing constipation.