Brief overview
- Lactose intolerance – Causes: Deficiency of the enzyme lactase, which is why lactose cannot be absorbed or can only be absorbed poorly. Instead, it is metabolized by intestinal bacteria, producing gases, among other things.
- Symptoms: Abdominal pain, diarrhea, flatulence, intestinal wind, bloating, nausea, nonspecific symptoms such as headache.
- Diagnosis: medical history, H2 breath test, diet/exposure test.
- Treatment: Adjustment of diet, avoidance of dairy products, lactase tablets
- Prognosis: lactose intolerance is not a disease and is not dangerous, but may limit quality of life.
Lactose intolerance: causes and triggers
Lactose intolerance is a form of food intolerance (food intolerance). Affected people cannot tolerate milk sugar (lactose) or can only tolerate small amounts of it. The reason for this is an enzyme deficiency:
Milk sugar (lactose) is a natural component of milk and dairy products, as well as being added to various other foods. It is a disaccharide and as such cannot be absorbed by the mucous membrane of the small intestine. To do so, it must first be broken down into its two components – the individual sugars galactose and glucose. These can then pass through the intestinal wall.
As a result, the lactose travels unchanged from the small intestine to the large intestine. There it serves as food for bacteria. This leaves waste products that trigger the typical symptoms. These waste products include lactic acids, short-chain fatty acids and gases such as hydrogen, carbon dioxide and methane.
Although the reason for lactose intolerance is ultimately always a deficiency of the enzyme lactase, this deficiency can occur in different ways. Accordingly, the symptoms vary in severity and may first appear at different ages.
Primary lactose intolerance
Primary lactose intolerance develops independently (in contrast to the secondary form). The underlying deficiency of lactase either develops naturally during adolescence (physiological lactase deficiency) or exists from birth (neonatal lactase deficiency):
Physiological lactase deficiency
Newborns can normally metabolize lactose without problems – they have to, because breast milk contains lactose (even more than cow’s milk). Therefore, the little body produces abundant amounts of the enzyme lactase, which is necessary for lactose utilization.
How much lactose is tolerated varies greatly from individual to individual and also depends on genetic predisposition. For example, while the majority of adult Africans and Asians are lactose intolerant, there are relatively few affected individuals among adult northern Europeans.
Neonatal lactase deficiency
This is a congenital lactose intolerance in babies – a very rare metabolic disorder. Due to a genetic defect, the body is either unable to produce any lactase at all from the beginning of life or can only produce tiny amounts. This is why it is also referred to as absolute lactose intolerance.
Affected babies get persistent diarrhea from their mother’s milk after only a few days. Breastfeeding is then not possible. Under certain circumstances, the undigested lactose can even pass through the stomach and intestinal mucosa directly into the bloodstream, where it can cause severe symptoms of poisoning. The only possible therapy is lifelong abstinence from lactose.
If newborns have problems with lactose, this does not necessarily have to be due to congenital lactose intolerance. The digestive tract in general can react very sensitively in the first weeks of life. Sometimes lactase production is not yet running smoothly, but usually this problem soon goes away.
Acquired (secondary) lactose intolerance
- Chronic inflammatory bowel disease such as Crohn’s disease
- Gastrointestinal infection
- gluten intolerance (celiac disease)
- Food allergies
Surgery to the gastrointestinal tract can also cause the patient to no longer tolerate lactose, or to tolerate it less well.
Secondary lactose intolerance may disappear again once the underlying cause has been successfully treated and the mucosal cells in the intestine have recovered (for example, from an intestinal infection).
Lactose intolerance: symptoms
The following symptoms typically occur in lactose intolerance once an individually intolerable amount of lactose ends up in the intestine:
- Bloated belly
- Feeling of fullness
- intestinal wind
- loud intestinal noises
- abdominal pain
- nausea, rarely with vomiting
- diarrhea
The flatulence and abdominal pain are caused by the gases produced by the bacteria in the large intestine during the decomposition of the undigested lactose. Other waste products produced in the process – namely lactic and fatty acids – have a “hydrophilic” effect. As a result, more fluid flows into the intestine and produces diarrhea.
Paradoxically, lactose intolerance can also lead to constipation. This is when the bacterial decomposition of lactose produces predominantly methane. This gas slows down intestinal activity, triggering intestinal sluggishness.
What influences lactose intolerance symptoms?
Degree of lactase deficiency
Behind lactose intolerance is a deficiency of the enzyme lactase. How pronounced this deficiency is varies greatly from person to person. Some sufferers produce virtually no lactase at all, which is why they often react sensitively to any intake of lactose. Others still have a certain amount of enzyme, so that they can tolerate at least small amounts of lactose.
Lactose content of the meal and other ingredients
Of course, the lactose content in a meal plays a crucial role. The more lactose it contains, the more severe the symptoms of lactose intolerance.
In addition, the other composition of the food also has an influence. This is because, depending on the other nutrients with which lactose is ingested, it can have a different effect on processing in the intestine. One example is sour milk products (such as yogurt or kefir): Although they contain a relatively high amount of lactose, they are still often well tolerated in lactose intolerance. The reason for this is the lactic acid bacteria, which are also present in abundance – they can break down larger quantities of lactose in the intestine.
Composition of the intestinal flora
Speed of food transport
The path that food takes during digestion is the same for all people. However, the time it takes is not. There are hardly any differences as far as the stomach, but how quickly the food pulp is transported through the intestine varies greatly from person to person.
This in turn has an influence on the lactose intolerance symptoms. This is because the longer the food pulp remains in the small intestine, the more time the lactase has to break down the milk sugar. If, on the other hand, it moves on quickly, more undigested lactose reaches the large intestine, where it causes the typical symptoms.
The duration of food transport through the small intestine varies approximately between one and two and a half hours, but in some people it even lies outside this range. Accordingly, the time after which lactose intolerance symptoms appear in those affected also varies.
Personal perception of pain
Every person perceives pain differently. Where some people go to the doctor long ago, others hardly notice anything. Even in the case of lactose intolerance, the discomfort feels different from person to person.
Lactose intolerance symptoms such as flatulence and abdominal pain can be more severe if sufferers hold back the sometimes foul-smelling intestinal gas in public out of shame. The gases, which cannot escape, stretch the intestinal wall, causing additional discomfort.
Lactose intolerance symptoms outside the gastrointestinal tract.
In addition to gastrointestinal symptoms, lactose intolerance may also cause the following symptoms:
- Headache
- Dizziness @
- Memory disorders
- listlessness
- Pain in the limbs
- acne
- depressive moods
- sleep disorders
- sweating
- Cardiac arrhythmias
While these lactose intolerance signs are not typical, in some cases they may occur in addition to gastrointestinal symptoms or even alone. In the latter case, the food intolerance is difficult to detect.
How lactose intolerance can cause symptoms outside the gastrointestinal tract in the first place is still under discussion. One possible explanation is that the bacterial breakdown of lactose in the large intestine produces toxic metabolites that enter the blood. These could cause problems in various body structures (especially nerve tissue).
Lactose intolerance: Diagnosis
In addition, everyone has flatulence and abdominal pain from time to time, so these symptoms are often not associated with lactose intolerance for a long time and are not always immediately recognized as lactose intolerance symptoms by doctors either.
Lactose intolerance: When to see a doctor?
If you observe persistent gastrointestinal complaints in yourself or your child, you should always go to the doctor to find the cause. The right person to contact if you suspect lactose intolerance is your family doctor or a specialist in internal medicine.
Medical history
First of all, the doctor will ask you in detail about your symptoms, any previous illnesses and the medication you are taking. In this way, he takes your medical history (anamnesis), which can give him initial clues about the possible causes of your complaints. Possible questions the doctor may ask include:
- What exactly are your complaints?
- How long have you had such complaints?
- Do symptoms such as abdominal pain, bloating and diarrhea occur after eating certain foods (such as dairy products)?
- Are there any known cases of food intolerances such as lactose intolerance in your family?
- Do you have a gastrointestinal condition (e.g. Crohn’s disease, celiac disease, stomach flu)?
- Are you taking any medications? If yes, which ones?
Physical examination
The medical history interview is followed by a physical examination. The doctor listens to the abdomen with a stethoscope to assess bowel sounds. He also gently palpates the abdomen. The main purpose of the physical examination is to rule out other causes for the symptoms. If necessary, further examinations may also be necessary, for example, a determination of the inflammation levels in the blood or an ultrasound examination of the abdomen.
Lactose intolerance test
If the doctor suspects lactose intolerance as the cause of your symptoms, he or she may suggest a diet or omission test followed by a stress test to clarify the situation: To do this, you must first avoid milk and dairy products for a certain period of time. Then you will be given a lactose solution to drink to see how your body reacts to it.
Also possible is a lactose tolerance test with blood sugar measurement before and after drinking a defined lactose solution. If you cannot metabolize lactose, your blood sugar level will not rise due to the drinking solution.
However, the so-called hydrogen breath test (H2 breath test) is most commonly used to diagnose lactose intolerance. It is based on the fact that intestinal bacteria also produce hydrogen gas when they break down lactose. This can be detected in the exhaled air.
Lactose intolerance: Treatment
With a low-lactose or lactose-free diet – adapted to the individual lactose tolerance – the symptoms of lactose intolerance can usually be avoided or at least reduced. If you do want to enjoy a piece of cream cake or a milk ice cream, you can take a preparation containing the enzyme lactase beforehand. This prevents complaints.
Secondary lactose intolerance can often be completely eliminated if the underlying disease can be successfully treated.
Lactose intolerance: diet
In the case of lactose intolerance, it is important to adjust the diet in such a way that no or at least as few symptoms as possible occur. To this end, the body should only be fed as much lactose as it can tolerate. How much that means in concrete terms can only be found out by trial and error. Each person has a different tolerance level for lactose. Some people with lactose intolerance have to avoid lactose very strictly (for example, in the case of neonatal lactase deficiency). However, many can at least metabolize small amounts of lactose.