Food allergy and intolerance

What is a food allergy

Medical professionals speak of a food allergy when the body’s own immune system reacts to certain proteins in food with so-called IgE (immunoglobulin E) antibodies. This means that your immune system has usually formed memory cells for specific protein structures in a food. When you eat the food again, these IgE antibodies recognize the supposed enemy and try to fight it off. It is not the food, but the excessive and misguided response of the immune system that triggers the symptoms in these patients.

In the case of intolerance, there is no excessive response from the immune system (no specific IgE antibodies detectable), but rather a lack of certain enzymes in your intestine that reduce the absorption or digestion of certain food components – the body is then unable to break down these substances (such as lactose in the case of lactose intolerance or histamine in the case of histamine intolerance) sufficiently quickly, which leads to an accumulation and the associated symptoms. For example, if you experience abdominal pain or diarrhea after eating a certain food, this is usually an indication of a non-allergic intolerance.

Food allergy: causes and risk factors

It is estimated that around five percent of the population suffer from a food allergy. As with any other allergy, the cause of the excessive reaction is a malfunction of your immune system, which defends itself against specific, harmless proteins, so-called allergens. Babies mainly develop allergies to basic foods – such as milk, chicken eggs, soy or wheat. Food allergies in adolescents and adults tend to be to fruit, vegetables, spices, nuts or seafood.

Medicine distinguishes between a primary and a secondary food allergy. Pre-existing conditions are risk factors in each case: Primary food allergy usually occurs in early childhood. Children suffering from neurodermatitis are usually affected. The secondary form occurs predominantly in adults who are already allergic to pollen; here a cross-reaction between the allergy-triggering pollen proteins and proteins occurring in a similar form in the corresponding foods leads to a reaction of the immune system – a so-called cross-allergy.

The most common primary food allergies

• Peanut allergy and tree nut allergy: Allergies to peanuts and tree nuts occur in childhood but often persist into adulthood. If you suffer from a peanut allergy, you need to be particularly careful, as you often react to even minimal traces of the allergen. Nowadays, special blood tests can be used to make a certain risk assessment. Peanuts belong to the legume family; cross-reactions are therefore more likely with soy or lupin flour than with actual nuts. These in turn sometimes show cross-reactions with each other. Nuts must be mentioned in the list of food ingredients. It usually says “nuts”.
• Fish allergy: People with a fish allergy also often have severe reactions. In some cases, even if they only inhale fish vapor. In most cases, they do not respond to all fish species, but only to certain ones.
• Chicken egg allergy: A child’s chicken egg allergy usually disappears by school age. If a child tolerates baked egg, this has a positive effect on the overall development of tolerance.
• Cow’s milk allergy: In 60 to 80 percent of cases, the allergy to cow’s milk resolves by the time the child reaches school age. In baked form (as an ingredient in dough and the like), 75 percent of children allergic to cow’s milk tolerate milk earlier.
• Soy allergy: Soy is also one of the most common triggers of food allergies in children. In our culture, it usually comes to light when parents give their children who suffer from a cow’s milk allergy soy milk as a substitute. As mentioned, patients with soy allergy sometimes show cross-reactions with peanut. In most cases, the primary soy allergy disappears spontaneously by the age of ten.
• Wheat allergy: Hives, vomiting or respiratory problems are symptoms of children who are allergic to wheat. In Europe, around 0.3 percent of all children under the age of five suffer from it. It usually subsides by the time they are teenagers. In adults, however, there is sometimes a special form – the exertion-dependent wheat allergy: symptoms only occur if there is additional physical exertion after eating wheat.

Secondary food allergies are mostly cross-allergies

A cross allergy is a side effect of hay fever. If you are allergic to the pollen of grasses and trees, this can be coupled with reactions to vegetables and fruit. This is because certain proteins in the pollen that trigger hay fever have a similar structure to proteins in some types of fruit and vegetables. For example, people who are allergic to birch pollen can also show an immune response to pome fruit and stone fruit such as apples, pears, peaches, almonds and hazelnuts.

A latex allergy can be a cross-reaction to an allergy to the houseplant birch fig (Ficus benjamini).

Allergies to house dust mites can also lead to cross-reactions with seafood or invertebrates (e.g. fish parasites, snails, edible insects).

Symptoms: Food allergies manifest themselves in very different ways

Allergic complaints to food can occur on the skin and mucous membranes, affect the ear, nose and throat area, the lungs or the gastrointestinal tract.

This is usually an immediate-type allergy. This means that the allergic symptoms appear within a few minutes of coming into contact with the allergen. Only rarely do symptoms only appear hours later. They usually affect the skin, for example in the form of a worsening of atopic eczema (neurodermatitis) and are a late type IV allergy.

Most common symptoms: Discomfort on the skin

Skin complaints such as redness, swelling, wheals or eczema are the result of every second allergy to food.

Occasionally: respiratory symptoms

Runny nose, sneezing attacks, coughing, phlegm and even asthma are among the occasional symptoms of a food allergy.

Rare symptoms: reactions in the mouth

Swelling of the lips, palate or tongue combined with itching are rare allergic reactions to food. Sometimes food allergies affect the gastrointestinal tract. Then you get flatulence, abdominal pain, diarrhea, nausea and vomiting or constipation.

For some allergy sufferers, even minimal amounts of a food can trigger a strong allergic reaction. For example, traces of peanuts in muesli. In the worst case, anaphylaxis, i.e. allergic shock, may occur.

Alcohol, physical exertion and stress can increase the symptoms of a food allergy.

Diagnosis of food allergy

Diagnosing a food allergy and discovering the potentially critical foods can be difficult. On the one hand, there are a large number of possible triggers, and on the other hand, it is sometimes difficult to distinguish them from other, non-allergic intolerance reactions.

Medical consultation

A detailed discussion with us forms the basis of the diagnosis (anamnesis). We will ask you if:

• known allergies are present,
• Parents or siblings in your family suffer from allergies,
• you are taking medication,
• you suffer from other diseases,
• you feel psychologically burdened.

In preparation for the interview, it makes sense to keep a food diary in which you record the time:

• What exactly you ate and drank,
• whether symptoms occurred afterwards,
• whether you were taking medication,
• whether there were any other abnormalities,
• whether the symptoms appeared under physical stress.

Skin test or blood test

In order to determine more clearly whether a food allergy is actually present and which substances are the trigger, we at the USZ usually carry out an allergy test afterwards. Here too, the prick test is the standard procedure. However, unlike for allergens that you inhale, there are no standardized test solutions available for food. For this reason, the test is sometimes carried out with the suspected food itself; we may therefore ask you to bring food that you consider to be allergenic to the test. However, you must be aware that the results of the prick test are only of limited significance.

Therefore, in addition to skin tests, a blood test is an important diagnostic tool. Several test methods are available for this purpose, of which the determination of specific IgE antibodies is the most important. The laboratory diagnosis of food allergies has become highly refined in recent years and allows very precise conclusions to be drawn about cross-allergies, hidden allergens and in some cases also statements about the potential danger of an allergic tendency.

In the case of food intolerances, skin tests are unfortunately not conclusive; in some cases, blood tests or examinations by a gastrointestinal specialist are helpful (such as in the case of coeliac disease/gluten sensitivity or lactose intolerance). Skin tests and IgE determinations are only used here to differentiate from actual food allergies, such as fructose intolerance. Histamine intolerances can often only be diagnosed by ruling out other diseases, as there are still hardly any reliable laboratory tests available.

Elimination diet and provocation test

If the previous interviews and tests are inconclusive, an elimination diet can provide clarity. To do this, avoid foods or ingredients suspected of causing allergies for up to two weeks. If your symptoms improve or disappear completely, we can then carry out a provocation test with individual allergens. This involves swallowing the food or allergen in question under medical supervision. If your symptoms reappear, then the allergen has been found. It is often possible to estimate the amount of an allergen that is still tolerated or to determine that a certain food can be enjoyed again despite a positive allergy test.

Such elimination diets or provocation tests can also be very valuable for detecting or ruling out intolerance reactions to food, for example in the case of histamine or lactose intolerance.

Food allergy: prevention, early detection, prognosis

Many parents are concerned with the question of how they can prevent allergic diseases in their children, especially if there is already a family history of allergies. You cannot prevent a food allergy, but you can promote the development of your child’s tolerance. Above all, do not avoid certain foods during pregnancy in anticipatory obedience.

How you can prevent a food allergy in your child

• Pediatricians recommend breastfeeding children for five to six months. You should introduce complementary foods from the age of five months. A varied diet gradually introduces babies to as many foods as possible and, according to the latest findings, is also the best way to prevent allergies.
• Eat fruit and vegetables and follow a Mediterranean diet.
• Make sure you consume oils with long-chain omega-3 fatty acids.
• Consume full-fat dairy products, especially yogurt.
• Studies do not indicate that the risk of allergies in children is reduced if mothers follow special diets during pregnancy and breastfeeding.

Apart from nutrition, it helps the baby if its mother does not smoke and does not spend time in smoky rooms. If there are already allergies in the family, you should not get a cat. However, it is no longer recommended to give away an existing cat. Pregnant women should also avoid exposure to air pollutants and mold.

How you can avoid an allergic reaction yourself

• Eat processed rather than raw foods. Some allergens, which are mainly found in fruit and some vegetables, lose their risk potential if you heat, chop or acidify them.
• Study the allergen labeling on the food packaging.
• Ask about hidden allergy triggers (such as milk, egg, wheat, soy or celery) when you buy unpackaged, processed foods (for example, bread from the bakery).
• Ready-made products, sauces, puddings and delicatessen salads may also contain hidden allergens.
• Avoid foods such as cheese, yeast, spinach and red wine, as they contain histamine and can increase an allergic reaction.
• Be careful if you suffer from a severe chicken egg protein allergy and are due to be vaccinated. This is because some vaccines are bred from chicken eggs; in most cases, however, vaccination is still possible even in cases of severe chicken egg allergy, subject to certain precautions and medical supervision.

Prognosis of the food allergy

The course of a food allergy depends on the age at which the first allergic symptoms appeared. If they start in infancy, there is a good chance that they will regress by the age of six. The prognosis for adults is less favorable. Your food allergy is likely to persist for a long time, sometimes for the rest of your life.

Food allergy: treatment through abstinence

If you suffer from a food allergy (food allergy), the most important part of your treatment is to eliminate the allergenic food(s). avoid. Medical professionals refer to this as a restricted diet.

According to the Federal Department of Home Affairs from 2016, manufacturers are obliged to list the most common allergens on packaged goods. so that those affected can avoid the respective allergens.