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23 August 2023, Petra Orzech

What you should know about food intolerances

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You snack on grapes and get a bloated belly. You drink a glass of milk and suddenly have to go to the toilet. Or you suddenly have a headache after a tuna salad.

How can that be? Maybe you don't tolerate certain foods.


Food and drink supply our body with vital energy and building material. The digestive tract has the task of processing the ingredients from food in such a way that they are absorbed by the body and non-usable food residues are excreted.

The digestive system has no choice: it really has to process everything we "ingest". If the selection, composition and quantity of food does not correspond to what our system has been optimised for in the course of evolution, problems can arise.

In the past, fresh fruit and vegetables were practically only available at harvest time. Now we can buy them all year round. In addition, newer apple varieties, for example, are bred for higher fructose content because they taste sweeter.

50 years ago, there were hardly any ready-made meals either. But most of these products contain lactose, skimmed milk powder, lactose, fructose and glutamate. Anyone who has a food intolerance gets "inexplicable" complaints after eating such products.

Today, we not only consume numerous new substances through our food, but also ever larger quantities. As a result, food intolerances are steadily increasing.

What is the difference between intolerance and allergy?

Experts distinguish between an allergy and a food intolerance. In the case of an allergy, the body's immune system recognises certain components in food as the "enemy" and reacts with allergic reactions, such as itching and a skin rash.

In intolerances, the immune system is not involved. The problems result from a deficiency of certain enzymes in the intestinal system. This deficiency causes food components to enter the large intestine undigested. There they are metabolised by bacteria. The degradation products that result are the trigger for a number of complaints.

The intolerances are fructose, lactose, gluten and histamine intolerances. What does this mean in detail:

Fruit sugar intolerance (fructose intolerance)

In the case of fructose intolerance, an enzyme deficiency ensures that fructose cannot be completely broken down and then transported away via the blood system. This is how the fructose gets into the large intestine and is processed there by bacteria, which can then lead to complaints.

By the way: The complaints can be aggravated if diet, light and "sugar-free" products such as chewing gum or sweets are consumed at the same time. The sugar alcohols contained in these products worsen the tolerance of fructose.


Bloating, flatulence, abdominal pain and diarrhoea. There is also evidence that disorders in fructose metabolism are responsible for psychological conditions such as depression and anxiety. These in turn trigger more frequent cravings for sweets. If foods containing fructose are now consumed, the mood may be brightened for a short time, but in the long term this feeds a personal vicious circle.


During the decomposition process of the bacteria in the large intestine, hydrogen (H2) is produced, among other things. This enters the bloodstream and can also be measured in the breath. A doctor can tell you from a breath test whether you are fructose intolerant or not.


Once you have been diagnosed, you should discuss your eating habits with a nutritionist. With her help, you can adapt your diet to your circumstances. A food diary is an important and helpful component in this process. Normally, you do not have to completely avoid fructose. The important thing is to find out how much fructose you are intolerant to. However, you should avoid fructose-rich foods such as dried fruits, fruit juices, honey and fructose-enriched convenience products.

Lactose intolerance

As with the metabolisation of fructose, lactose (milk sugar) also requires a specific enzyme. This enzyme, called lactase, breaks down the milk sugar into galactose (mucilage sugar) and glucose (simple sugar), which is then passed from the intestine into the blood. The enzyme is produced in the small intestine. If there is a lactase deficiency, the lactose passes undigested into the large intestine without being broken down. There, the bacteria break down the lactose. The gases that form during this process can lead to pain.

Babies can usually still metabolise lactose well. However, this ability usually decreases over the years. But it is not only age that has an influence here. Geographical factors also play a role: in Scandinavia, about 5% of the population is intolerant. While in the Mediterranean region it rises to up to 70%.


Bloating, abdominal pain, diarrhoea and nausea.


As with fructose - via a breath test at the doctor's.


There are two options here:

1. avoidance of all foods containing lactose, especially dairy products. Alternatively, there is a wide range of lactose-free dairy products that can be consumed today. By the way, lactose is also a popular additive in ready-made meals. It is therefore advisable to take a look at the ingredients. Also take a look at the package inserts of your medicines: lactose is often used as a filler.

2. take lactase, the missing enzyme, about 30 minutes before eating. This way, the missing enzyme can be replaced and the symptoms do not occur.

Gluten intolerance (coeliac disease)

Most intolerance reactions to bread and cereals (wheat, spelt, rye, green spelt, barley, oats) are probably caused by gluten. "Gluten" is a collective term for various components of the so-called gluten protein, which is responsible for the good baking properties of cereals.

Gluten intolerance is a special case: It is neither an allergy nor a classic intolerance. With coeliac disease, the body reacts with an inflammation of the intestinal mucosa. The body's own defence system sees gluten as an enemy and triggers an immune reaction in the intestinal mucosa. The result is an inflammatory process.


The symptoms can be very different. Sometimes no complaints occur (silent coeliac disease). However, most of the time, in addition to digestive complaints such as irritable bowel syndrome, abdominal pain, diarrhoea and/or constipation, complaints also show up that are often not associated with food: Fatigue and concentration problems after eating, depression, movement disorders, infertility and susceptibility to infections.


The diagnosis of coeliac disease can be made on the one hand by determining antibodies (Ak determination) in the blood and on the other hand by taking tissue samples from the small intestine during a colonoscopy. Ideally, both examinations should be carried out.


Gluten intake should be less than 10 milligrams per day. This corresponds to a gluten-free diet. Since this is usually difficult to adhere to, a specially trained dietician should be consulted in any case. By the way, potatoes, millet, buckwheat, amaranth, rice, quinoa and maize are gluten-free.


New research shows that more and more people react to wheat with symptoms but do not have coeliac disease. The symptoms are similar to those of coeliac disease and can affect the digestive tract, but also completely different organs. According to current knowledge, a diet low in gluten has a positive effect. In this context, it is recommended to inform yourself about a so-called "low FODMAP diet". In simple terms, this involves reducing the intake of certain carbohydrates. It is assumed that this changes the composition of the intestinal flora and strengthens the protective function of the intestinal mucosa.

Histamine intolerance 

Histamine is a substance that is produced in the body itself and can also be supplied with food. Presumably, some people can break down histamine from food more slowly or only incompletely. Enzymes also seem to play a role here.


If histamine intolerance causes the body to be flooded with histamine, the first and most common symptom is the so-called "curse": the face and neck suddenly become red and burning hot. Severe headaches, circulatory problems, rapid heartbeat and a drop in blood pressure as well as abdominal cramps and diarrhoea are also common.


Histamine intolerance is currently difficult to prove. Thus, the diagnosis is mainly based on observations and the symptoms that occur. The probability of an intolerance is high if the above-mentioned symptoms occur after eating histamine-containing foods such as alcohol, tuna, salami, parmesan, sauerkraut and other "matured" foods.

Intolerance of the flavour enhancer glutamate as well as intolerance of foods that release histamine, such as strawberries or tomatoes, are also indications of histamine intolerance.


The aim of the treatment is to restore the balance between histamine intake and histamine breakdown. There are various possibilities for this, which are best worked out individually with an allergist and nutritionist.

In case you're wondering…

… to what extent dietary supplements would be helpful in cases of intolerance: It is important to remember that food supplements themselves often cause intolerance - even if they actually promise relief. Sometimes they can even intensify the symptoms. If you suspect you are suffering from an intolerance, the first thing to do is to stop taking all food supplements. By the way, unlike medicines, food supplements are not subject to any kind of control and there is almost no industry-independent research in this area.

... what are the effects of probiotic preparations?

By taking preparations with so-called "good" bacteria, you will at best achieve a temporary improvement of the symptoms. If, on the other hand, you avoid the incompatible food (ingredients), the "bad" bacteria are starved out. This allows the "good" bacteria to multiply again. It is important to create the conditions for your individual balance of intestinal bacteria to develop. This requires time, patience and competent care.


If you suspect a food intolerance, it is useful to

  1. keep a food diary
  2. seek the help of a nutrition expert
  3. Eat naturally and in moderation - intermittent fasting is also a good idea.
  4. Give your intestines lots of love and patience.


Following the theme: Eat as if your life depended on it - because it does.