What are food allergies?
Food allergy is a form of food hypersensitivity. Additionally, when the person allergic symptoms after eating a certain food that a healthy person tolerates normal.
In the classification, which uses the "World Allergy Organisation" in food hypersensitivity, any allergic reaction is accompanied with an activation of the immune system. All other reactions fall under the concept of non-allergic food hypersensitivity. The latter reactions are known as food intolerance.
Food allergy is distinguished in IgE-mediated and non-IgE-mediated. IgE-mediated food allergy can be divided into primary and secondary-or cross allergy. A special form is anaphylactic reaction, acute, life-threatening allergic reaction. Anaphylaxis is usually IgE-mediated.
In general, food allergies more common in young children than in adults, in whom the immune system has not yet come to full development.
IgE-mediated food allergies
Most food allergies are IgE-dependent.
The allergy occurs in two stages. Is a person allergic to the food, then takes place at the first place a contact sensitization. Has any food allergens that are repetitive in their form characteristic of that food. In the awareness-raising phase the body makes IgE antibodies (IgE's) to which such a form, that they fit exactly to the allergens.
In a subsequent intake occurs in the second phase, in which the allergy manifested by symptoms. This second phase with allergic symptoms, however, does not occur for anyone who is already sensitized. Estimated that only gets about half complaints.
Allergic reactions are first certain substances like histamine. These released substances are then responsible for the earliest occurring symptoms: redness, swelling, contraction of smooth muscle and mucus production. After several hours, an inflammatory reaction occurs by infiltration of inflammatory cells (eosinophils, neutrophils) into the tissues. This reaction can last for a few days.
Primary- or non-cross-reactive food allergy
Here there is an allergic reaction to a single type of allergen. However, it is possible to have multiple allergies primary at the same time.
Secondary-or kruisreactieve food allergy
Even here there is first a sensitization to the allergen that is specific to the particular food. In the second phase, however, is not only responded to repeated contact with the same allergen, but also on allergens of other nutrients or non-nutrients that are about the same shape. Such an Exchange might take place between berkepollen and apples or between latex (natural rubber) and bananas. The cross allergies can also start with a response to a non-food item, for example first latex and then bananas. It is striking, that this is not as strong to both the sides work out. Someone with a latex allergy has about 30% chance of a cross allergies with food, while someone with a food allergy has 15% chance on a latex allergy.
Anaphylaxis
Anaphylaxis, a mostly IgE-mediated food allergy, is a serious, life-threatening, generalized or systemic hypersensitivity reaction. In the vast majority of cases the cause is eating peanuts or nuts. However, this often leads to death. Also here is the person concerned first sensitized. At a following ingestion of the allergen gets the person suffer from acute distress and among other things a sharp drop in blood pressure. Anaphylaxis is caused not only by food allergy, but also, for example, by medications, insektensteken or respiratory sensitisers.
At a direct administration of adrenaline Anaphylaxis is important to the reaction to stop and prevent serious consequences.
Non-IgE-mediated food allergies
These are very rare. This particularly concerns enteropathy in young infants, where the babies have severe intestinal problems. Are rare in infants also enterocolitis and proctocolitis for.
Non-IgE-dependent food allergies caused by immune reactions in which IgG, IgM and IgA can be involved, caused by immune complexes which consist of food components and antibodies, and by cell-dependent immunity.
Causes of food allergy
Primary food allergies are generally caused by a small number of foods. In children are milk, eggs, peanuts, tree nuts and fish responsible for three-quarters of all food allergies; in adults are peanuts, tree nuts, wheat, soy, fish and shellfish the main causes.
Above eight foods are together account for 90 percent of all food allergies. In addition it comes also allergy to fruits and vegetables relatively common.
By this small number of kinds of primary allergens one would expect, that an allergy is easy to prevent. However, there are some reasons why a food allergy (increasing) problem is:
- It is the most important allergy-causing proteins are intentionally added by the food industry to food, in order to modify its properties. Such as milk protein in yogurt, soups and sauces; soy protein of excipients (for example, emulsifiers); chicken protein to banquet.
- The allergens are easily accidentally in our diet right. In the food industry, where multiple production lines are in contact with each other or raw materials are not quite pure; home, which contains food or household utensils unwanted allergens.
- Transmission in physical contact, such as children, caring hands, kissing.
- Reaction to allergens other substances which have approximately the same shape and therefore cause a cross allergy.
Symptoms that often occur with food allergy
- Oral Allergy Syndrome (especially hay fever)
- Respiratory Complaints
- Digestive Complaints
- Skin complaints
- Complaints concerning cardiovascular
- Rash over the whole body
- Swollen eyes
- Thick throat
Food allergy test
In order to demonstrate food allergy, there are several methods available.
Elimination diet
An elimination diet is the traditional method to investigate food allergies or intolerances. In the first phase, the patient should only eat food which is very unlikely to cause allergies. The complaints are then disappear. In the second phase, one at a feed added to the diet. When returning the complaint back then it is clear which food caused. For the patient, the elimination diet is a demanding and time-consuming diet. Also to be all sorts of potentially allergenic foods purchased for testing, which costs may entail. Many doctors prescribe, if after following an elimination diet seems to have become clear what the allergen, a provocation diet. It found the suspected food is deliberately taken to verify the findings of the elimination diet were correct, so that the appropriate allergen is detected.
Skin tests
There are two types of skin tests: the prick test and intradermal test. In the first, the allergen applied to the skin, and there is then incised, in the intracutaneous test, the allergen with a needle injected superficially in the skin. As a check is also the pure dissolving fluid and a solution of histamine inserted at both tests. After about fifteen minutes, an allergy can be determined on the basis of the skin reaction. The prick test is inexpensive, easy to apply and has a high specificity. The intradermal test is more expensive to apply a more complicated, but is approximately 1,000 to 10,000 times more sensitive. However, the quality of the skin test is highly dependent on the quality of the test substances used. The self-prepared test substances give in comparison to the commercial preparations is usually the best results.
Blood test for food allergies
An alternative to the skin test is a blood test. By the amount of IgE Antigen in the blood to measure that is specific to a particular allergen, food allergies can be determined belonging to type I allergy. Disadvantage is that this research is much more expensive than the skin test. Examples of blood tests are RAST and ELISA. Type IV allergies include food allergies to be using the elimination diet diet tested.
Measuring IgG/IgG4 to diagnose food allergy is not meaningful. A link between IgG/IgG4 and what allergy is no evidence to support these claims. It is also the case that in healthy people after a meal always food-specific IgG and IgG4 is formed. Tests for food-specific IgG, for any condition makes sense, except for food-induced pulmonary hemosiderose (Heiner syndrome, very rare, bleeding in the lungs of children).