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Food allergy

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 In medicine, food allergy is an immunologic response to a food protein. It is estimated that up to 2 million Americans have food allergies of one type or another [1], and the prevalence is rising [citation needed]. 6-8% of children have food allergies and 2% of adults have them [2]. The most common food allergies in adults are shellfish, peanuts, tree nuts, fish, and eggs [2]. In children, they are milk, eggs, and peanuts [2].

At this time, there is no cure for food allergy. Some food allergies tend to get worse over a lifetime [citation needed], because it is almost impossible for an individual to completely avoid contact with an allergen.

Treatment consists of avoidance diets, where the allergic person avoids any and all forms of the food that they are allergic to. Food allergy is distinct from food intolerance, which is not caused by an autoimmune reaction.

Persons diagnosed with a food allergy may carry an epi pen, wear a medic alert bracelet, or develop an emergency action plan, in accordance with their doctor.

Signs and symptoms

Symptoms of food allergies include [3]:

Angioedema is a skin reaction where the tissues swell. It can result in swelling/edema of the lips, skin tongue and airways (causing constriction, wheezing and difficulty breathing). It can also cause swelling of the face, eyes, hands, etc...

The symptoms of an allergic reaction can develop immediately or up to an hour after ingestion of the allergen [2].

Food allergy can lead to anaphylactic shock: A systemic reaction involving several different bodily systems including hypotension (low blood pressure) and loss of consciousness. This is a medical emergency. Allergens commonly associated with this type of reaction are peanuts, nuts, milk, egg, and seafood. [citation needed] Food anaphylaxis can also be caused by various types of fruit.[1] Latex products can induce similar reactions.

Food allergy is thought to develop more easily in patients with the atopic syndrome, a very common combination of diseases: allergic rhinitis and conjunctivitis, eczema and asthma. [citation needed] The syndrome has a strong inherited component; a family history of allergic diseases can be indicative of the atopic syndrome.

Another type of food allergy is called Gastrointestinal Food Hypersensitivity. [citation needed] It can be IgE or Non-IgE mediated.

In this class, IgE mediated responsese include:

  • Immediate GI Hypersensitivity
  • Oral allergy syndrome

Conditions that have been shown to have both IgE and Non-IgE causes of gastrointestinal food hypersensitity include: [citation needed]

  • Alleric eosinophilic esophagitis
  • Allergic eosinophilic gastritis
  • Allergic eosinophilic gastroenteritis

Conditions of Non-IgE gastrointestinal food hypersensitivity include: [citation needed]

  • Enterocolitis syndrome
  • Dietary protein proctitis
  • Celiac Disease

The Big Eight

The most common food allergies are [1]:

These are often referred to as "the big eight." [citation needed] They account for over 90% of the food allergies in the United States of America [4] [5]. Sesame is currently the 9th most common food allergen in America according to the Food Allergy and Anaphylaxis Network. [citation needed] Yet virtually any food can be a food allergen. According to the website of pediatric authors Dr. Sears, berries, buckwheat, chocolate, cinnamon, citrus fruits, coconut, corn, mustard, peas, pork, seeds, sesame, sugar, tomatoes and yeast are also common allergens. The Joneja Food Allergen Scale shows the relative allergenicity of various foods.[6]

Likelihood of allergy can increase with exposure[citation needed]. For example, rice allergy is more common in Asian nations where rice forms a large part of the diet[citation needed]. In Central Europe, celery allergy is more common. The top allergens vary somewhat from country to country but milk, eggs, peanuts, treenuts, fish, shellfish, soy, wheat and sesame tend to be in the top 10 in many countries. [citation needed]

Diagnosis

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

There are two basic types of allergy tests: Skin Prick Tests and blood tests. The skin prick 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 stick 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.

Blood tests, such as RAST, measure the amount of IgE antibodies, and are another useful diagnostic tool. In RAST, blood is drawn and sent to a lab for testing. Researches have been able to determine "predictive values" for certain foods. These predictive valuse 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.[7] 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.

Blood testing by ELISA methodologies is the only method currently available that can measure antibodies of types IgE and IgG. IgG-type anitbodies are implicated in a wide variety of food allergy reactions including rheumatoid arthritis [8] diarrhea, and constipation, among others.

Diagnostic tools for gastrointestinal food hypersensitivity often 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 specific proteins such as gliadin (present in wheat and other grains).
  • Irritable bowel syndrome (IBS); although many IBS cases might be due to food allergy, this is an important diagnosis in patients with diarrhea in whom no allergens can be identified.
  • C1 esterase inhibitor deficiency (hereditary angioedema); this rare disease generally causes attacks of angioedema, but can present solely with abdominal pain and occasional diarrhea.

Pathophysiology

Further information: 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.

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. Flu vaccines and the Yellow Fever vaccine are still egg-based. [citation needed] As of 1994, Measles-Mumps-Rubella vaccine no longer uses eggs.[9] There is resistance to this theory, especially as it applies to autoimmune disease.[10]

Another theory focuses on whether an infant's immune system is ready for complex proteins in a new food when it is first introduced.[11]

The most popular theory at this time is the Hygiene Theory. [citation needed] Researches speculate [citation needed] that in the modern, industrialized nations, such as the United States, food allergy is 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 theory is based partly on studies showing less allergy in third world countries. [citation needed] Research has found [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.

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) 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 allergy. [citation needed] There are no allergy desensitization or allergy "shots" available for food allergy. [citation needed]

According to experts at the BA Festival of Science in Norwich, England, vaccines can be created using genetic engineering to cure allergies. If this can be done, food allergies could be eradicated in about ten years.[12]

Statistics

For reasons that are not entirely understood, the diagnosis of food allergies has become more common in Western nations in recent times (this trend seems to apply to asthma as well). In the United States, it is believed that about 4% of the population suffers from food allergies. [citation needed] In children, this number is believed to be significantly higher. It is estimated that more than 100,000 Australian children have undiagnosed food allergies. [citation needed]

The most common food allergens include peanuts, milk, eggs, tree nuts, fish, shellfish, soy, and wheat - these foods account for about 90% of all allergic reactions. [citation needed]

Differing views

Various medical practitioners have a differing views on food allergies. Irritable Bowel Syndrome (IBS) patients have been studied with regards to food allergies. Some studies have reported on the role of food allergy in IBS; only one epidemiological study on functional dyspepsia and food allergy has been published. The mechanism by which food activates mucosal immune system is uncertain, but food specific IgE and IgG4 appeared to mediate the hypersensitivity reaction in a subgroup of IBS patients. Exclusion diets based on skin prick test, RAST for IgE or IgG4, hypoallergic diet and clinical trials with oral disodium cromoglycate have been conducted, and some success has been reported in a subset of IBS patients.[13]

Studies comparing skin prick testing and ELISA blood testing have found that the results of skin prick testing correlate poorly with hypersensitivity demonstrated directly through dietary challenge. [14]

Extensive clinical experience has demonstrated significant improvement of patients with IBS whose ELISA-based food allergy testing is positive and where treatment includes a careful exclusion diet. [15]

In addition, many practitioners of complementary and alternative medicine ascribe symptoms to food allergy where other doctors do not. The causal relationships between these various conditions and food allergies have not been studied extensively enough to provide sufficient evidence to become authoritative. The interaction of histamine with the nervous system receptors has been demonstrated, but more study is needed.[16] Other immune response effects are commonly known (swelling, irritation, etc.), but their relationships to some conditions has not been extensively studied. Examples are arthritis, fatigue, headaches, and hyperactivity. Nevertheless, hypoallergenic diets reportedly can be of benefit in these conditions, indicating that the current medical views on food allergy may be too narrow. Holford and Brady (2005) suggest three levels of response; classical immediate-onset allergy (IgE), delayed-onset allergy (giving a positive response on an ELISA IgG test but rarely on an IgE skin prick test), and food intolerance (non-allergic), and claim the last two to be more common.[17] It is important to note that IgG is present in the body and is known to respond to foods. So some medical practitioners, especially allergists, state that there is no preditive value to these types of tests, despite the studies cited above.

In children

Milk and soy allergies in children can often go undiagnosed for many months, causing much worry for parents and health risks for infants and children. Many infants with milk and soy allergies can show signs of colic, blood in the stool, reflux, rashes and other harmful medical conditions. [citation needed] These conditions are often misdiagnosed as viruses or colic.

Many children who are allergic to cow's milk protein also show a cross sensitivity to soy-based products. [citation needed] There are infant formulas in which the milk and soy proteins are degraded so when taken by an infant, their immune system does not recognize the allergen and they can safely consume the product.

About 50% of children with allergies to milk, egg, soy, and wheat will outgrow their allergy by the age of 6. For those that don't, and for those that are still allergic by the age of 12 or so, have less than an 8% chance of outgrowing the allergy [18].

Peanut and tree nut allergies are less likely to be outgrown, although evidence now shows [citation needed] that about 20% of those with nut allergies do eventually outgrow the allergy. In such a case, they need to consume nuts in some regular fashion to maintain the non-allergic status. [citation needed] This should be discussed with a doctor.

See also

Footnotes

  1. ^ a b http://www.aaaai.org/patients/publicedmat/tips/foodallergy.stm
  2. ^ a b c d National Institute of Allergy and Infectious Diseases (2004). "NIH Publication No. 04-5518: Food Allergy: An Overview" (PDF). p. 35. {{cite web}}: Unknown parameter |month= ignored (help)
  3. ^ http://www.nlm.nih.gov/medlineplus/ency/article/000817.htm
  4. ^ http://www.foodallergy.org/allergens/index.html
  5. ^ http://www.askdrsears.com/html/4/t041800.asp
  6. ^ "Joneja Food Allergen Scale". J.A. Hall Publications. - Note that to read the scale, you compare items within each column; position across columns is not significant
  7. ^ Sampson JACI 1997 & 2001 and Garcia-Ara JACI 2001
  8. ^ M Hvatum, L Kanerud, R Hällgren and P Brandtzaeg. (2006) The gut–joint axis: cross reactive food antibodies in rheumatoid arthritis; Gut 2006;55:1240-1247. PMID: 16484508.
  9. ^ drgreene.com
  10. ^ sciencedaily.com
  11. ^ nutritionandeggs.co.uk
  12. ^ "Food allergies 'gone in 10 years'". BBC News. 2006-09-09. Retrieved 2006-09-09.
  13. ^ Park MI, Camilleri M. (2006). Is there a role of food allergy in irritable bowel syndrome and functional dyspepsia? A systematic review. Neurogastroenterol Motil. 2006 Aug;18(8):595-607. PMID: 16918724
  14. ^ Zar, Sameer; Benson, Martin J.; Kumar, Devinder (2005). Food-specific serum IgG4 and IgE titers to common food antigens in irritable bowel syndrome. Am J Gastroenterol. 2005 Jul;100(7):1550-7.
  15. ^ Wangen, Stephen O. The Irritable Bowel Syndrome Solution. 2006. ISBN 0976853787. Excerpted with author's permission at The IBS Treatment Center
  16. ^ Wood, J.D. (2006) Histamine, mast cells, and the enteric nervous system in the irritable bowel syndrome, enteritis, and food allergies. Gut. 2006 Apr;55(4):445-7.
  17. ^ Patrick Holford and James Braly (2005). Hidden Food Allergies: Is What You Eat Making You Ill? Piatkus Books. ISBN 0-7499-2602-3.
  18. ^ FAAN conference notes, March 2006
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