Letzte Aktualisierung am 7. December 2023 von Dr. Michael Zechmann-Khreis
Various symptoms of lactose intolerance
The symptoms of lactose intolerance are very varied. The most common symptoms are flatulence, diarrhea, nausea and abdominal pain. In order to understand how and why these symptoms occur when lactose is consumed, it is necessary to understand the structure and pathway of lactose. Read here about the symptoms of lactose intolerance.
Lactase breaks down lactose
The enzyme lactase is produced in the small intestine and breaks down lactose (the milk sugar, a disaccharide) into its two monosaccharides. These are then absorbed into the body in the small intestine. If this enzyme is missing or is only insufficiently produced, this is referred to as lactose maldigestion or, subsequently, lactose intolerance. This is because the lactose is then not broken down, cannot be absorbed in the small intestine and ends up in the large intestine.
Bacteria break down the lactose
Intestinal bacteria are found in the large intestine. That’s quite normal and that’s how it should be. These bacteria can break down the lactose. In people without lactose intolerance, no lactose reaches the other sections of the intestine, as it has already been absorbed by the body. This means that the bacteria do not get any lactose as “food”. If you have lactose maldigestion, the lactose enters this area of the intestine and the bacteria break it down. In the process, they produce hydrogen (H2), short-chain fatty acids andCO2. Many other substances can be formed, depending on the type of bacteria. These include various alcohols or even sulphurous compounds. Among other things, these substances lead to the symptoms mentioned above. If symptoms occur, this is known as lactose intolerance.
How the symptoms of lactose intolerance develop
TheCO2 and the other gases produce symptoms such as flatulence and a bloated stomach, the short-chain fatty acids (acetic acid, butyric acid, …) change the osmotic conditions in the intestine and lead to fluid penetration into the intestinal lumen. This causes the stool to liquefy, resulting in watery diarrhea. There is also nausea and other symptoms of discomfort, but almost never vomiting.
The symptoms of lactose intolerance include
- Feeling of fullness
- Flatulence, intestinal winds
- Bloated belly
- Loud bowel sounds, “bubbling” in the bowel
- Abdominal pain
- Watery diarrhea / constipation
In some patients, the bacteria in the large intestine produce methane instead of hydrogen. This gas slows down intestinal movements. This can also cause constipation instead of diarrhea. The methane also leads to extreme flatulence and severe abdominal pain due to the stretching of the intestines.
However, there are also patients who may exhibit the above symptoms for reasons other than food intolerance. It is therefore important to have a test carried out by a doctor if you suspect that you have an intolerance. In a trial in 1995, 30 people were tested who claimed to suffer from lactose intolerance and showed severe symptoms after drinking milk. 9 of these patients turned out not to be lactose intolerant, i.e. they were able to digest lactose without any problems.
Suarez F.L., Savaiano D.A., Levitt M.D: A Comparison of Symptoms after the Consumption of Milk or Lactose-Hydrolyzed Milk by people with Self-Reported Severe Lactose Intolerance, N Engl J Med. 1995 Jul 6;333(1):1-4.
Medow et al: Lactose Intolerance. New England Journal of Medicine 333 (1995): 1358-1359
Ledochowski M., Bair H., Fuchs D.: Lactose intolerance. J Ernährungsmed. 1/2003 (2003): 7-14