Food intolerances

Food intolerances are a general term for all reactions that occur in connection with the consumption of food and typically lead to local symptoms in the digestive tract. However, some types of food intolerance can also affect other organs such as the skin, respiratory tract, and nervous system, or present as generalized malaise.

A basic distinction is made between immunologically mediated and non-immunologically mediated food intolerances. The latter make up the majority of all adverse food reactions.

In most of these cases, an enzyme deficiency forms the basis of the intolerance, which means that food components such as milk sugar (lactose intolerance) or histamine (histamine intolerance) cannot be adequately broken down. In the case of fructose or sorbitol intolerance, however, the absorption of these carbohydrates by the small intestinal epithelium is limited.

Fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) are another group of carbohydrates that are poorly absorbed in the small intestine and therefore fermented by bacteria in the colon. As a result of these fermentation processes, gases (hydrogen H₂, carbon dioxide CO₂, methane CH₄) are produced, which can cause intestinal symptoms such as bloating, abdominal pain, and diarrhoea.

Foods considered high in FODMAPs include:

• Cereal products (wheat, barley, rye)
• Dairy products containing lactose
• Fruits with high fructose content
• Sugar substitutes (sorbitol, maltitol, mannitol, xylitol, isomalt)

In all of these overreactions to specific foods, the immune system plays no role, as all components in the food are generally tolerated by the immune system and do not lead to the activation of immune cells.

In contrast, with immunologically mediated food intolerances, all components of the food can be digested and absorbed by the body, but certain food components stimulate immune cells. The resulting inflammatory reactions are similar to the ones that occur in the biologically meaningful defence against pathogens. In this case, however, they target harmless macromolecules or the body’s own structures, which leads to allergies or autoimmune reactions (e.g. coeliac disease).

In classic food allergies, a sensitization phase always precedes the actual allergic inflammation after contact with the food, during which the affected person shows no symptoms. Due to a dysregulation of the immune system, renewed or continued contact with the allergen immediately leads to symptoms such as swelling, itching, or shortness of breath. A key event in immediate-type allergies is the excessive production of allergen-specific IgE antibodies.

The most common triggers of IgE-mediated food allergies include:

• Peanuts
• Tree nuts
• Soya
• Fish
• Shellfish
• Cow’s milk
• Wheat
• Hen’s egg

However, there are also immunologically mediated food allergies that do not represent a "true" allergy, as they are not IgE-mediated. These include:

• Pseudoallergy

The term pseudoallergy refers, in a narrower sense, to all immediate-type reactions caused by immune system malfunctions that are not mediated by sIgE antibodies.

• Autoimmune coeliac disease

Coeliac disease is a chronic inflammatory autoimmune condition of the intestine.

• Non-coeliac wheat sensitivity

Non-coeliac wheat sensitivity is usually present when symptoms similar to coeliac disease or wheat allergy occur but cannot be attributed to an autoimmune or allergic reaction.

As well as:

• IgG-associated food reactions

These reactions occur when an excess of food-specific IgG antibodies is formed, which cross the intestinal barrier and enter the bloodstream.

A wide range of laboratory tests is available for the detection of allergies or intolerances (intolerance testing) through the analysis of stool samples, blood samples, or breath tests. The compilation of a detailed medical history, followed by an elimination diet, can help affected individuals achieve symptom relief and reduce discomfort in the long term.