Testing food intolerance

Many people in western industrialized nations suffer from food intolerance (NMU). This often leads to pain after eating, abdominal cramps, nausea and diarrhea. Many triggers are known that can lead to an intolerance to certain food components. This article explains what intolerances there are and how to test whether you have a food intolerance.

What is food intolerance?

Food intolerance is a generic term for disease symptoms that are caused by the consumption of food. Food allergies should be distinguished from food intolerances. Allergies are mediated by the immune system, but the immune system does not play a role in food intolerance. The causes of food intolerances lie elsewhere. They are triggered by enzyme defects (e.g. lactose intolerance) or targeted reactions to certain substances (e.g. histamine intolerance).

What tests are there for different forms of food intolerance?

Food intolerances are triggered by various mechanisms. For this reason, there are also a variety of tests to determine the intolerance. The type of test depends on the type of food intolerance.

Test for lactose intolerance (lactose intolerance)

The intolerance to lactose (lactose intolerance) is very common. It is based on a reduced to completely absent activity of the enzyme lactase, which is responsible for the breakdown of lactose in the intestine. Such a lack or reduced enzyme activity occurs in up to three quarters of the world population. The lactose can then not be split in the intestine and can be absorbed. As a result, it is converted from bacteria in the intestinal flora to carbon dioxide (CO₂) and hydrogen (H₂). These gases are absorbed through the intestinal wall, transported to the lungs via the blood and released with the exhaled air. This phenomenon is used in the diagnosis of lactose intolerance.

With the so-called H₂ breath test, the patient is given a certain amount of lactose (usually 50 grams, in children one to two grams per kilogram of body weight). The hydrogen in the exhaled air is then measured. If there is a large amount of hydrogen in the exhaled air, there is a suspicion of lactose intolerance. The limit here is usually 20 ppm (“parts per million” is a way of specifying concentrations). In addition, symptoms such as flatulence and abdominal pain are observed throughout the test period.

Since a defect in the gene for lactase is the most common trigger for lactose intolerance, this intolerance can also be determined by a genetic test. However, such an examination is more expensive than the H₂ breath test. Either the health insurance company approves the test or you have to pay for it yourself.

Test for fructose intolerance (fructose intolerance)

This form of food intolerance is caused by an inadequate function of a fructose transporter. This defective function can be due to either a reduced number or a malfunction of the transporter. The transporter, which is called GLUT-5, lies in the lining of the intestine. It ensures that fructose can enter the body through the mucous membrane.

With fructose intolerance, an H₂ breath test can also be used. It works on the same principle as the H₂ test used to diagnose lactose intolerance.

In addition, fructose intolerance can be determined using a fructose stress test. As part of this test, the patient ingests a large amount of fructose on an empty stomach, for example a large glass of naturally cloudy apple juice. Then they observe whether symptoms appear within the next few hours. The patient can initially carry out such a test at home. If symptoms occur, they should consult a doctor in order to confirm the diagnosis using the H₂ tests.

Test for histamine intolerance (histamine intolerance)

Histamine is mainly found in foods that have undergone a ripening process. These include cheese, red wine, sauerkraut and many more.

The release of histamine plays an important role in the development of allergies. However, histamine can trigger symptoms without the presence of an allergy. When consuming large amounts of histamine (for example in spoiled fish), there may be signs of intoxication. It is controversial whether even small amounts of histamine can trigger intolerance reactions.

Some patients report that foods containing histamine can cause nausea, abdominal pain, but also allergy-like symptoms such as itching, runny nose, watery eyes, shortness of breath and dizziness. Whether these symptoms are really triggered by histamine is controversial among researchers and there is currently no clear evidence for it.

One theory of why some people do not tolerate large amounts of histamine is related to the enzymes that break down histamine. These are so-called dioxidases (DOA). Reduced activity of these enzymes could be the reason for histamine intolerance. The activity of DOA can be determined from blood using laboratory tests. However, some experts regard these blood tests as unusable. If histamine intolerance is suspected, the first thing that is recommended instead is a low-histamine diet, in which one can observe whether the symptoms subside.

What other food intolerance tests are there?

There are two other test methods that are easy to perform and are useful for diagnosing most food intolerances:

• Provocation tests
• Elimination tests

Provocation test for food intolerance

Provocation tests are based on a simple test principle: If there is a suspicion that a particular food causes an intolerance reaction, the patient ingests that food and observes whether a reaction occurs. Such foods can be identified, for example, by keeping a food diary. Patients note down exactly what they eat and how they feel after eating. Provocation tests are easy to do. Nevertheless, they should always be done in consultation with the doctor, as symptoms such as nausea, abdominal pain, abdominal cramps and diarrhea can occur.

Elimination tests for food intolerance

In some ways, an elimination test is the opposite of a provocation test. Here, food is gradually removed that is suspected of causing an intolerance reaction. If symptoms improve, it can be assumed that one of the omitted foods is actually responsible for this reaction.

Which doctors can I carry out an intolerance test with?

As the first point of contact, the family doctor can advise on incompatibilities and refer you to specialists if necessary:

1. Internists and gastroenterologists

1. Lactose intolerance (breath test)
2. Fructose intolerance (breath test)
3. Sorbitol intolerance (breath test)
4. Celiac disease / gluten intolerance (IgA antibodies)

2. Dermatologist

1. Food allergy test on the skin (e.g. skin prick test)
2. IgE antibody testing for allergies (blood test)
3. Histamine intolerance (DAO)

Food intolerances are very common. They represent a great burden for those affected. They experience strong symptoms and an enjoy their food less. However, there are a number of tests to find the cause of the food intolerance.