food allergies

More rare food allergies

Likelihood of allergy can increase with exposure[citation needed]. For example, rice allergy is more common in East Asia where rice forms a large part of the diet.[13]

In Central Europe, celery allergy is more common. In Japan, allergy to buckwheat flour, used for Soba noodles, is more common.

Red meat allergy is extremely rare in the general population, but a geographic cluster of people allergic to red meat has been observed in Sydney, Australia.[14] There appears to be a possible association between localised reaction to tick bite and the development of red meat allergy.

Fruit allergies exist, such as to apples, pears, jackfruit, strawberries, etc.

Corn allergy may also be prevalent in many populations, although it may be difficult to recognize in areas such as the United States and Canada where corn derivatives are common in the food supply.[15]

[edit] Diagnosis

The best method for diagnosing food allergy is to be assessed by an allergist. The allergist will review the patient's history and the symptoms or reactions that have been noted after food ingestion. If the allergist feels the symptoms or reactions are consistent with food allergy, he/she will perform allergy tests.

Examples of allergy testing include:

* Skin prick testing is easy to do and results are available in minutes. Different allergists may use different devices for skin prick testing. Some use a "bifurcated needle", which looks like a fork with 2 prongs. Others use a "multi-test", which may look like a small board with several pins sticking out of it. In these tests, a tiny amount of the suspected allergen is put onto the skin or into a testing device, and the device is placed on the skin to prick, or break through, the top layer of skin. This puts a small amount of the allergen under the skin. A hive will form at any spot where the person is allergic. This test generally yields a positive or negative result. It is good for quickly learning if a person is allergic to a particular food or not, because it detects allergic antibodies known as IgE. Skin tests cannot predict if a reaction would occur or what kind of reaction might occur if a person ingests that particular allergen. They can however confirm an allergy in light of a patient's history of reactions to a particular food. Non-IgE mediated allergies cannot be detected by this method.

* Blood tests are another useful diagnostic tool for evaluating IgE-mediated food allergies. For example, the RAST (RadioAllergoSorbent Test)detects the presence of IgE antibodies to a particular allergen. A CAP-RAST test is a specific type of RAST test with greater specificity: it can show the amount of IgE present to each allergen.[16] Researchers have been able to determine "predictive values" for certain foods. These predictive values can be compared to the RAST blood test results. If a persons RAST score is higher than the predictive value for that food, then there is over a 95% chance the person will have an allergic reaction (limited to rash and anaphylaxis reactions) if they ingest that food.[citation needed] Currently, predictive values are available for the following foods: milk, egg, peanut, fish, soy, and wheat.[17][18][19] Blood tests allow for hundreds of allergens to be screened from a single sample, and cover food allergies as well as inhalants. However, non-IgE mediated allergies cannot be detected by this method.

* Food challenges, especially double-blind placebo-controlled food challenges (DBPCFC), are the gold standard for diagnosis of food allergies, including most non-IgE mediated reactions. Blind food challenges involve packaging the suspected allergen into a capsule, giving it to the patient, and observing the patient for signs or symptoms of an allergic reaction. Due to the risk of anaphylaxis, food challenges are usually conducted in a hospital environment in the presence of a doctor.

* Additional diagnostic tools for evaluation of eosinophilic or non-IgE mediated reactions include endoscopy, colonoscopy, and biopsy.

Important differential diagnoses are:

* Lactose intolerance; this generally develops later in life but can present in young patients in severe cases. This is due to an enzyme deficiency (lactase) and not allergy. It occurs in many non-Western people.
* Celiac disease; this is an autoimmune disorder triggered by gluten proteins such as gliadin (present in wheat, rye and barley). It is a non-IgE mediated food allergy by definition.
* Irritable bowel syndrome (IBS)
* C1 esterase inhibitor deficiency (hereditary angioedema); this rare disease generally causes attacks of angioedema, but can present solely with abdominal pain and occasional diarrhea.

[edit] Pathophysiology
For more details on this topic, see allergy.

Generally, introduction of allergens through the digestive tract is thought to induce immune tolerance. In individuals who are predisposed to developing allergies (atopic syndrome), the immune system produces IgE antibodies against protein epitopes on non-pathogenic substances, including dietary components.[citation needed] The IgE molecules are coated onto mast cells, which inhabit the mucosal lining of the digestive tract.

Upon ingesting an allergen, the IgE reacts with its protein epitopes and release (degranulate) a number of chemicals (including histamine), which lead to oedema of the intestinal wall, loss of fluid and altered motility. The product is diarrhea.[citation needed]

Any food allergy has the potential to cause a fatal reaction.

[edit] Causes

The immune system's eosinophils, once activated in a histamine reaction, will register any foreign proteins they see. One theory regarding the causes of food allergies focuses on proteins presented in the blood along with vaccines, which are designed to provoke an immune response. Influenza vaccines and the Yellow Fever vaccine are still egg-based, but the Measles-Mumps-Rubella vaccine stopped using eggs in 1994.[20] However large scientific studies do not support this theory, especially as it applies to autoimmune disease.[21]

Another theory focuses on whether an infant's immune system is ready for complex proteins in a new food when it is first introduced.[22]

One hypothesis at this time is the Hygiene hypothesis. While there is no proof for the hygiene hypothesis, people speculate[citation needed] that in modern, industrialized nations, such as the United States, food allergies are more common due to the lack of early exposure to dirt and germs, in part due to the over-use of antibiotics and antibiotic cleansers. This hypothesis is based partly on studies showing less allergy in third world countries.[citation needed] Some research suggests[citation needed] that the body, with less dirt and germs to fight off, turns on itself and attacks food proteins as if they were foreign invaders.

Antibiotics have also been implicated in Leaky Gut Syndrome which is another possible cause of food allergies[citation needed].

A lower incidence of food allergies in the developing world could also be due to differences in diet from the West and less exposure to food allergens.

Others have found that food allergies are due to widespread usage of baby skin-care products that contain allergens, such as lotions based upon peanut oil. These skin-care products are cheaper to manufacture than non-allergenic ones and using them sensitizes the baby, which later develops into a food allergy. This theory has yet to come with sufficient explanation as to why the occurrence of allergies has been on a steady rise in the last two decades.

[edit] Prevention

According to a report issued by the American Academy of Pediatrics, "There is evidence that breastfeeding for at least 4 months, compared with feeding infants formula made with intact cow milk protein, prevents or delays the occurrence of atopic dermatitis, cow milk allergy, and wheezing in early childhood."[23]

[edit] Treatment

The mainstay of treatment for food allergy is avoidance of the foods that have been identified as allergens.

If the food is accidentally ingested and a systemic reaction occurs, then epinephrine (best delivered with an autoinjector of epinephrine such as an Epipen or Twinject) should be used. It is possible that a second dose of epinephrine may be required for severe reactions.[citation needed] The patient should also seek medical care immediately.

At this time, there is no cure for food allergies.[24] There are no allergy desensitization or allergy "shots" available for food allergies.[citation needed] Some doctors feel they do not work in food allergies because even minute amounts of the food in question or even food extracts (as in the case of allergy shots) can cause an allergic response in many sufferers.

Ronald van Ree of Amsterdam University expects that vaccines can in theory be created using genetic engineering to cure allergies. If this can be done, food allergies could be eradicated in about ten years.[25]