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In medicine, food allergy is hypersensitivity to dietary substances, leading to various types of gastrointestinal complaints. It occurs mainly, but not exclusively, in children. It is a common type of allergy, and is usually treated with an exclusion diet. Food allergy is distinct from food intolerance, which is not caused by an autoimmune reaction.
Signs and symptoms
Symptoms of the peanut allergy include:
Hives/urticaria/wheals (small raised itchy areas likened to bites)
Itchy red skin, rashes
Congested runny nose
Pain in the stomach, vomiting, nausea, diarrhea
Swelling/edema of the lips, skin tongue and airways (causing constriction, wheezing and difficulty breathing)
Shock (as blood pressure drops and the blood struggles to pump blood around the body.)
The symptoms usually develop within half an hour of ingesting the allergen.
Rarely, food allergy can lead to anaphylactic shock: 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 seafoods. 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. The syndrome has a strong inherited component; a family history of these diseases can be indicative of the atopic syndrome.
Diagnosis
The best method for diagnosing food allergy is to be assessed by an allergist. The allergist will discuss the symptoms that occurred after the food ingestion. If the allergist feels the reaction is in keeping with a real food allergy, he/she will perform allergy skin tests. These skin tests are performed by a method called skin prick testing, which is a somewhat uncomfortable test tolerated by most adults but not all children. The results are available within 15 minutes. Another option is to perform blood testing, called RAST testing, for the foods that are suspected as allergens. ELISA tests for IgE may also be used.
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 a specific wheat protein (gliadin).
- 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
See also allergy for a general discussion of the background of 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. 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.
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. As of 1994, Measles-Mumps-Rubella vaccine no longer uses eggs.* There is resistance to this theory, especially as it applies to autoimmune disease.*
Another theory focuses on whether an infant's immune system is ready for complex proteins in a new food when it is first introduced.*
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 in an Epipen) should be used. It is possible that a second Epipen dose may be required for severe reactions. The patient should seek medical care.
At this time, there is no allergy desensitization or allergy "shots" available for food allergy.
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. In children, this number is believed to be significantly higher.
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.
Differing views
Various medical specialties have a differing view on food allergies. What is called irritable bowel syndrome by many doctors (a stress-related functional disorder) is often interpreted by allergists to be food allergy.
In addition, many practitioners of complementary and alternative medicine ascribe symptoms to food allergy where most classically trained doctors would not find a causal relationship. Examples are headaches, tiredness and hyperactivity. Nevertheless, hypoallergenic diets can be of benefit in these conditions, indicating that the current medical views on food allergy may be too limited. 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.
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. 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. 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.
See also
External links
References
Patrick Holford and James Braly (2005). Hidden Food Allergies: Is What You Eat Making You Ill? Piatkus Books. ISBN 0749926023.
Allergology | Gastroenterology | Immunology
Nahrungsmittelallergie | 食物アレルギー | Voedselallergie en voedselintolerantie | Alergia alimentar
"Food allergy"