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Food Allergies

Food Allergies

Definition

Food allergies are the body's abnormal responses to harmless foods; the reactions are caused by the immune system's reaction to some food proteins.

Description

Food allergies are often confused with food intolerance. However, the two conditions have different causes and produce different symptoms. A food allergy is also known as food hypersensitivity. The allergy is caused when a person eats something that the immune system incorrectly identifies as harmful.

Food allergies

About 4% of adults have food allergies according to the National Institute of Allergy and Infectious Diseases (NIAID). The condition affects approximately 6 to 8% of children age 4 and younger.

The immune system works to protect the body and creates food-specific antibodies. The antibodies are proteins that battle antigens, substances that are foreign or initially outside the body. The introduction of an antigen produces the immune response. Antibodies are created to destroy the antigen or counteract its effectiveness.

The food that triggered that reaction is called an allergen. The antibodies are like an alarm system coded to detect the food regarded as harmful. The next time the person eats that food, the immune system discharges a large amount of histamine and chemicals. This process meant to protect the body against the allergen causes an allergic reaction that can affect the respiratory tract, digestive tract, skin, and cardiovascular system.

Allergic reactions can occur in minutes or in up to two hours after the person ate the food. Symptoms include swelling of the tongue, diarrhea, and hives. In severe cases, the allergic reaction can be fatal. The most severe reaction is anaphylaxis, which could be life-threatening.

Food intolerance

While food allergies involve the immune system, food intolerance is not related to the immune system. For example, a person who is lactose intolerant has a shortage of lactose, the digestive enzyme that breaks down the sugar in milk and dairy products. That person could experience stomach pain or bloating several hours after drinking milk.

People who are food-intolerant can sometimes consume that food and not experience intolerance symptoms. Those diagnosed with food allergies must avoid the foods that produce the allergic reactions.

Allergy-producing foods

Although approximately 160 foods produce allergic reactions, approximately 90% of reactions are caused by some or all items within eight food families. These are milk, eggs, peanuts, tree nuts, fish, shellfish, wheat, and soy. These foods can cause severe reactions. The most adverse reactions are caused by peanuts and tree nuts. According to NIAID, about 0.6% of Americans are impacted by peanut allergies. Approximately 0.4% of Americans have allergic reactions to tree nuts.

Food allergy demographics

Most children have allergies to eggs, milk, peanuts or tree nuts, and soy, according to the American Dietetic Association (ADA). The young generally outgrow their allergies. They are more likely to outgrow milk and soy allergies, according to NIAID. However, children and adults usually allergic to peanuts and tree nuts for life. The most frequent causes of food allergies in adulthood are peanuts, tree nuts, fish, and shellfish.

Allergies are hereditary. There is a tendency for the immune system to create IgE antibodies in people with family histories of allergies and allergic conditions like hay fever and asthma, according to NIAID. The likelihood of a child having food allergies increases when both parents are allergic.

Furthermore, people are allergic to the foods that are eaten frequently in their countries. A rice allergy is more common in Japan, and codfish allergies occur more in Scandinavian countries, according to NIAID.

Causes and symptoms

Food allergies are caused by the immune system's reaction to a food item that it believes is harmful. When the food is digested, the immune system responds by creating immunoglobulin E (IgE) antibodies as a defense. The antibodies are proteins found in the bloodstream. Formed to protect the body against harmful substances, the antibodies are created after the person's first exposure to the allergen.

The majority of food allergies are caused by foods in eight families. In some families, every food causes an allergic reaction. In other families like shellfish, a person may be allergic to one species, but able to eat others. The allergy-inducing foods include:

  • Milk. The dairy family includes milk, ice cream, yogurt, butter, and some margarines. Nondairy foods that contain casein must be avoided. Prepared foods that contain milk range from breads and doughnuts to sausage and soup, according to the ADA.
  • Eggs. Although a person may be allergic to either the egg white or yolk, the entire egg must be avoided because there is a risk of cross-contamination. Eggs are an ingredient in mayonnaise. Moreover, products such as baked goods, breads, pasta, yogurt, and batter on fried foods may contain eggs. In addition, some egg-substitute products contain egg whites.
  • Peanuts grow in the ground and are legumes like lentils and chickpeas. A person with a peanut allergy may not be allergic to other legumes or tree nuts. Products to be avoided include peanuts, peanut butter, peanut oil, and some desserts and candy. In addition, some Asian dishes are prepared with a peanut sauce. Tree nuts include almonds, cashews, pecans, walnuts, Brazil nuts, chestnuts, hazelnuts, macadamia nuts, pine nuts, pistachios, and hickory nuts. Products containing tree nuts include nut oil, nut oil, desserts, candy, crackers, and barbecue sauce. A person may be allergic to one type of nut but able to eat other nuts. That should be determined after consulting with a doctor.
  • Fish allergy is generally diagnosed as an allergy to all fish species because the allergen is similar among the different species.
  • Shellfish species include lobster, crab, shrimp, clams, oysters, scallops, mollusks, and crawfish. An allergy to one type of shellfish may indicate an allergy to others.
  • Wheat is a grain found in numerous foods including breads, cereals, pastas, lunch meats, desserts, and bulgar. It is also found in products such as enriched flour and farina.
  • Soy. The soybean is a legume, and people who have this allergy are rarely allergic to peanuts or other legumes. Soy is an ingredient in many processed foods including crackers and baked goods, sauces, and soups. There is also soy in canned tuna, according to the ADA.

The chemical reaction

During the initial exposure, many IgE antibodies are created. These attach to mast cells. These cells are located in tissue throughout the body, especially in areas such as the nose, throat, lungs, skin, and gastrointestinal tract. These are also the areas where allergic reactions occur.

The antibodies are in place, and a reaction is triggered the next time the person eats the food regarded as harmful. As the allergen reacts with the IgE, the body releases histamine and other chemicals. Histamine is a chemical located in the body's cells. When released during an allergic reaction, histamine and other chemicals cause symptoms like inflammation.

The type of allergic reaction depends on where the antibodies are released, according to NIAID. Chemicals released in the ears, nose, and throat could cause the mouth to itch. The person may also have difficulty breathing or swallowing. If the allergen triggers a reaction in the gastrointestinal tract, the person could experience stomach pain or diarrhea. An allergic reaction that affects skin cells could produce hives. This condition also known as urticaria is an allergic reaction characterized by itching, swelling, and the presence of patchy red areas called wheals.

Severe allergic reaction

Anaphylaxis is a severe allergic reaction that is potentially life-threatening. Also known as an anaphylactic reaction, this condition requires immediate medical attention. The reaction occurs within seconds or up to several hours after the person ate the allergy-inducing food.

Symptoms can include difficulty breathing, a tingling feeling in the mouth, and a swelling in the tongue and throat. The person may experience hives, vomiting, abdominal cramps, and diarrhea. There is also a sudden drop in blood pressure. Anaphylaxis could be fatal if not treated promptly.

Each year, some 150 Americans die from foodinduced anaphylaxism, according to NIAID. The casualties are generally adolescents and young adults. The risk increases for people who have allergies and asthma. Also at increased risk are people who experienced previous episodes of a naphylaxis.

The peanut is one of the primary foods that trigger an anaphylactic reaction. Tree nuts also cause the reaction. The nuts generally linked to anaphylaxis are almonds, Brazil nuts, cashews, chestnuts, hazelnuts, macadamia nuts, pecans, pine nuts, pistachios and walnuts. Fish, shellfish, and eggs can also set off the reaction, according to the ADA.

Cross-reactivity

Cross-reactivity is the tendency of a person with one allergy to reaction to another allergen. A person allergic to crab might also be allergic to shrimp. In addition, someone with ragweed sensitivity could experience sensations when trying to eat melons during ragweed pollinating season, according to NIAID. The person's mouth would start itching, and the person wouldn't be able to eat the melon. The cross-reaction happens frequently with cantaloupes. The condition is known as oral allergy syndrome.

Diagnosis

Food allergies are diagnosed by first determining whether a person has an allergy or if symptoms are related to a condition like food intolerance. The medical professional may be a board-certified allergist, a doctor with education and experience in treating allergies. However, some health plans may require that the patient first see a family practice doctor.

If food allergies are suspected, the doctor will take a detailed case history. The doctor asks the patient if there is a family history of allergies. Other questions are related to the patient's adverse reactions.

The doctor's questions include how the food was prepared, the amount eaten and what time the reaction happened. The patient describes the symptoms and actions taken to relieve them. The doctor also asks if the patient had other similar experiences when eating that food.

The patient receives a physical exam. In addition, the doctor may ask the patient to keep a food diary, a log of what the person eats for one to two weeks. The medical history and the food diary are used in conjunction with testing to diagnose the patient.

Allergy tests

Doctors generally start the testing process with a skin test or a blood test. The prick skin test, which is also known as the scratch test, examines the patient's reaction to a solution containing a protein that triggers allergies.

The doctor places a drop of the substance on the patient's arm or back. The doctor then uses a needle to prick or scratch the skin. This allows the potential allergen to enter the patient's skin. If more than one food allergy is suspected, the test is repeated with other proteins applied to the skin. After about 15 minutes, the doctor can read the reactions on the patient's skin.

If there is no reaction, the patient is probably not allergic to that food. The possibility of an allergy is indicated by the presence of a wheal, a bump that resembles a mosquito bite. The wheal signifies a positive reaction to the test. However, the test may show a false positive, which is a reaction to a food that does not cause allergies.

The skin test is not appropriate for people who are severely allergic or have skin conditions like eczema. Those people are given the RAST (radioallergosorbent test). This test measures the presence of food-specific IgE in the blood. After a sample of the patient's blood is taken, it is sent to a laboratory. The sample is tested with different foods. Levels of antibodies are measured, and the reactions to different proteins are ranked. While measurement systems may vary, a high ranking indicates a high number of antibodies. Lab results are generally completed within a week.

Results to this test may not be conclusive. A negative test may not have identified antibodies in the patient's blood. Positive results make it probable but not definite that the patient has allergies.

Costs for blood and skin tests will vary, with fees ranging from $10 to more than $300. Insurance may cover some of the cost. While both tests are reliable, they aren't 100% accurate. If questions remain, the diagnosis takes into account the patient's medical history and the food diary. If necessary, the patient is put on a special diet.

Elimination diet

If the skin or blood test shows strong positive results, the doctor may put the patient on an elimination diet. This is done when needed to narrow the list of suspected allergens. The person stops eating the foods suspected of causing the allergic reaction. That food is eliminated from the diet for from two to four weeks. If allergy symptoms improve, the food is probably an allergen.

If more confirmation is needed, the doctor may ask the patient to start eating the food again. The elimination diet procedure is generally not utilized if the patient initially had a severe reaction.

Food challenges

Other tests called food challenges may be performed. The challenges are done in a medical setting, with a doctor present. The patient is given capsules that each contain a different food. Some capsules contain allergy-producing foods. Other capsules may be placebos that won't produce a reaction.

The patient swallows the capsule, and the doctor watches for an allergic reaction. In an open food challenge, doctor and patient are aware of the capsule contents. In a single-blind food challenge, only the doctor knows. In a double-blind challenge, neither doctor nor patient knows the contents.

Challenges are rarely authorized by health care providers. Testing is time-consuming and many allergens are difficult to evaluate with the challenges, according to NIAID.

Treatment

The treatment for food allergies is to avoid eating the food that causes the allergy. This preventive treatment includes reading food labels. Manufacturers are required by the U.S. Food and Drug Administration to list a product's ingredients on the label. However, if there is a question about an ingredient, the person should contact the manufacturer before eating the food. When dining out, people should ask if food contains the allergen or ingredients contain the allergy-inducing foods.

When reading food labels, people with food allergies should know that:

  • Words indicating the presence of milk include lactose, ghee, and whey.
  • Words signifying eggs in a product include albumin, globulin, and ovomucin.
  • While it is apparent that peanuts are an ingredient in a product like peanut butter, there could be peanuts in hydrolyzed plant protein and hydrolyzed vegetable protein.
  • People with tree nut allergies should carefully read the labels of products such as cereals and barbecue sauce.
  • The American Dietetic Association cautions that surimi, an ingredient in imitation seafood, is made from fish muscle. Furthermore, fish in the form of anchovies is sometimes an ingredient in Worcestshire sauce.
  • Words on labels that signal the presence of wheat include gluten, sietan, and vital gluten.

Allergies and children

Parents of children with food allergies need to monitor their children's food choices. They also must know how to care for the child if there is an allergic reaction. Parents need to notify the child's school about the condition. Caregivers should be informed, too. Both the school and caregivers should know how to handle an allergic reaction. Care must be taken because a highly allergic person could react to a piece of food as small as 1/44,000 of a peanut kernel, according to NIAID.

Living with severe allergies

Despite precautions, people may accidentally eat something that causes an allergic reaction. People with severe allergies must be prepared to treat the condition and prevent an anaphylactic reaction. A medical alert bracelet should be worn. This informs people that the person has a food allergy and could have severe reactions.

To reduce the risks from an anaphylactic reaction, the person carries a syringe filled with epinephrine, which is adrenaline. This is a prescription medication sold commercially as the EpiPen auto injector. While prices vary, one syringe costs about $50.

The person with allergies must know how to inject the epinephrine. It is helpful for other family members to know how to do this, and parents of an allergic child must be trained in the procedure.

The person is injected at the first sign of a severe reaction. Medical attention is required, and the person should be taken to an emergency room. The person will be treated and monitored because there could be a second severe reaction about four hours after the initial one.

Allergy treatment research

There was no cure for food allergies as of the spring of 2005. That could change, with some relief available for people diagnosed with peanut allergies. According to a study reported on in 2003 in the New England Journal of Medicine, 84 people who took the drug TNX-901 had a decrease in their IgE antibody levels.

Organizations including the Food Allergy & Anaphylaxis Network (FAAN) lauded the results of the study that was conducted from July of 1999 through March of 2002. Work on that study was stopped in 2004 when biotechnology companies Genentech, Novartis, and Tanox concentrated efforts instead on use of an asthma medication for treating peanut allergies. Research started in June of 2004 on omalizumab, a medication sold commercially as Xolair. The study of Xolair's effectiveness was expected to take from two to three years.

Alternative treatment

The only treatment for food allergies is for a person to stop eating the food that causes the allergies. Some alternative treatments may be helpful in easing the symptoms caused by allergies. However, people should check with their health care providers before embarking on an alternative treatment.

Prognosis

Food allergies cannot be cured, but they can be managed. The allergen-inducing foods should be avoided. These foods should be replaced with others that provide the vitamins and nutrients needed for a healthy diet. Organizations including the American Dietetic Association recommend the following dietetic changes:

  • Milk is a source of calcium and vitamins A and D. For people with milk allergies, alternate choices of calcium include calcium-fortified orange juice and cereal.
  • Since eggs are an ingredient in products like bread, egg-free sources of grains are an alternate source of vitamin B.
  • Peanuts are a source of vitamin E, niacin, and magnesium. Other sources of these nutrients include other legumes, meat, and grains.
  • Fish is a source of protein and nutrients like B vitamins and niacin. Alternate sources of these nutrients should be sought.
  • Wheat is a source of many nutrients including niacin and riboflavin. The person allergic to wheat should substitute products made from grains such as oat, corn, rice and barley.
  • Although soybeans are rich in nutrients, very little soy is used in commercial products. As a result, a person with this food allergy would not need to find a safe substitute in order to get needed nutrients.

Prevention

People prevent the return of food allergies by following treatment guidelines. These include avoiding the foods that cause allergic reactions, reading food labels, and taking measures to prevent an anaphylactic reaction.

Anaphylaxisisamajor concern after a diagnosis of severe food allergies. To reduce the risks associated this reaction, people with food allergies should wear medical alert bracelets and never go anywhere without epinephrine. If possible, family members or friends of adults with allergies should learn how to administer this medication.

The American Dietetic Association advises people to develop an emergency plan. ADA recommendations include preparing a list of the foods the person is allergic to, three emergency contacts, the doctor's name, and a description of how to treat the reaction. This list is kept with the epinephrine syringe.

Resources

BOOKS

Freund, Lee and Rejaunier, Jeanne. The Complete Idiot's Guide to Food Allergies. Penguin Group, USA, 2003.

The American Dietetic Association. Food Allergies: How to Eat Safely and Enjoyably. John Wiley & Sons., 1998.

PERIODICALS:

ORGANIZATIONS

American Dietetic Association. 120 South Riverside Plaza, Suite 2000. Chicago, IL 60606-6995. 800-877-1600. http://www.eatright.org.

American Academy of Allergy, Asthma & Immunology. 555 East Wells Street Suite 1100, Milwaukee, WI 53202-3823. 414-272-6071. http://www.aaaai.org.

The Food Allergy & Anaphylaxis Network. 11781 Lee Jackson Highway, Suite 160, Fairfax, VA 22033. 800-929-4040. http://www.foodallergy.org.

National Institute of Allergy and Infectious Diseases. 6610 Rockledge Drive, MSC 6612, Bethesda, MD 20892-6612. 301-496-5717. http://www.niaid.nih.gov.

OTHER

Food Allergy An Overview. National Institute of Allergy and Infectious Diseases. July 2004. [cited March 30, 2005]. http://www.niaid.nih.gov/publications/pdf/foodallergy.pdf.

Peanut Anti-IgE Study Update. The Food Allergy & Anaphylaxis Network. September 2, 2004 [cited April 5]. http://www.foodallergy.org/Research/antiigetherapy.html.

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Food Allergies and Sensitivities

Food allergies and sensitivities

Definition

A food allergy or sensitivity is a person's immune system reaction to eating a particular food.

Description

The word allergy comes from two Greek words: alos, meaning "other" and argon, meaning "action." When one has an allergy, he or she has a reaction other than the one expected.

Food allergies and sensitivities are the body's reaction to a specific food. In a food allergy or sensitivity, when the child eats a particular food, (such as eggs, for example) usually by the time the eggs reach the stomach or the intestines, the body reads the presence of eggs as an allergen (something harmful). It sends out immunoglobulin E (IgE), an antibody, to destroy the eggs and protect the body, releasing histamines. The body remembers and produces histamines every time the food is eaten. These histamines trigger allergic symptoms that affect many areas of the body, particularly the skin, respiratory system, nervous system, and digestive system. Digestive disorders after eating specific foods are not always allergies. These reactions can be food sensitivities or intolerances. They can also be symptoms of other, more serious digestive diseases and malfunctions.

In the United states, 90 percent of all food allergies are caused by wheat, peanuts, nuts, milk, eggs, shellfish, soy, and fish. Many other foods can be at the root of food allergies or sensitivities, especially berries and other fruits, tomatoes, corn, and some meats like pork. Migraine headaches have been associated with sensitivities to chemicals contained in red wine, deli meats, aged cheeses, and the tannins in tea.

Usually, when a child is allergic to one food in a food family, he or she will most likely react to other foods in that food family. For example, if a child is sensitive to one type of fish, he or she also may be sensitive to other types of fish. This is called cross-reactivity.

Demographics

Nearly three million children in the United States have been diagnosed with food allergies. Nearly 600,000 of them have severe allergies to peanuts and possibly twice as many have severe shellfish allergies. Each year about 200 adults and children in the United States die from food-related anaphylaxis , an extreme reaction that causes swelling of the throat and bronchial passages, shock, and a severe drop in blood pressure. Nevertheless, food allergies tend to be under-diagnosed by doctors.

Genetics seems to play a part in food allergies. If one parent has a food allergy, the child's risk of having a food allergy is doubled. If both parents have food allergies, the risk is even higher. The child, however, may be allergic to a completely different food from the one to which the parent has demonstrated sensitivity. There also is increased risk when there are other kinds of allergy-related diseases in the family, such as hay fever or asthma .

Causes and symptoms

Causes

Allergies are caused by the immune system's reaction to a particular food. Usually, a child will have had a prior exposure before IgE or specific histamines are produced.

Food intolerance is often put into the same category as food allergy, even though there may be an entirely different mechanism involved. In these cases, the digestive tract reacts to a specific part of the food; for example, the protein or the sugar in a specific food. The digestive system rebels, resulting in gas, bloating, upset stomach, diarrhea , nausea , or vomiting . Many times, these responses are due to eating food contaminated with bacteria, rather than a true food allergy. In other cases, the child's reaction is due to an underlying digestive disorder such as irritable bowel syndrome , which is a chronic condition that is often triggered by specific types of food.

Gluten intolerance is not an allergy. It is a disease called celiac disease , or gluten-sensitive enteropathy. The body cannot process gluten found in wheat and other grains. Though the immune system is involved, celiac disease does not behave as a true allergy. Its treatment is like many food allergies, namely avoidance of the offending substance, which in this case is gluten.

Some children may lack a specific enzyme needed to metabolize certain foods. About 10 percent of all adults and older children have lactose intolerance . There are two forms of lactose intolerance: inherited and acquired. The inherited form (autosomal recessive) is extremely rare and severe. The acquired type is very common, and occurs in older children (not infants) and adults. It is distressing, but not life-threatening, and occurs with increased frequency in African Americans. Sometimes infants, as well as older children and adults, have a transient lactose deficiency after an episode of diarrhea.

Children with lactose intolerance have a lactase deficiency that keeps them from processing milk and milk products. These children can often drink milk that has had this enzyme introduced into the product. Some children can drink milk that has acidophilus bacteria put into it. This bacteria breaks down the lactose, or milk sugar, in the milk so that the child can tolerate it. Some children with lactose intolerance cannot drink whole milk, but can eat cheese or drink low-fat buttermilk in small quantities. This is different from a true milk allergy where even a small amount of any dairy product will produce a reaction.

Some children may also be intolerant of food colorings, additives, and preservatives. Among these are yellow dye number 5, which can cause hives ; and monosodium glutamate, which produces flushing, headaches, and chest pain . Sulfites, another additive, have been found to cause asthmatic reactions and even anaphylactoid reactions. Sulfites are preservatives used in wines, maraschino cherries, seafood, and soft drinks. They are sometimes put on fresh fruits and lettuce to maintain their fresh appearance, on red meats to prevent brown discoloration, and even in prepared deli foods like crab salad. Sulfites appear on food labels as sodium sulfite, sodium bisulfite, potassium bisulfite, sulfur dioxide, and potassium metabisulfite. The U.S. Food and Drug Administration (FDA) has banned the use of sulfites as a preservative for fruits and vegetables, but they are still in use in some foods.

Symptoms

Food allergies and sensitivities can produce a wide range of symptoms involving the skin, respiratory system, and nervous system. Children may have watery eyes, runny noses, and sneezing.

Skin rashes or hives can range from measles-like rashes to itchy welts. The rashes or welts can appear on a specific part of the body or can be widespread. Some children have swelling of the eyes, lips, and/or tongue.

Symptoms vary among children, even those who are sensitive to the same food. One child's specific reaction to an offending food does not mean that all children react the same. Nut allergies and shellfish, however, seem to be the most documented triggers for anaphylaxis. Nevertheless, anaphylaxis is not limited to those foods. IgE-mediated allergic reactions can progress to other allergic symptoms. For example, a child who has had hives is at risk for angioedema (swelling of the blood vessels) and anaphylaxis.

Symptoms also vary in intensity and by the amount eaten. One child may have a mild rash on the forearms when eating half a dozen strawberries. Another may be covered with a rash after eating only one. This variation is individualized and is a factor in the body's sensitivity to the target food.

Although the time between ingestion and symptoms is somewhat variable for allergic reactions (IgE-mediated), the vast majority occur within minutes. Nearly all occur within two hours. Reactions due to intolerances, like lactose, may occur somewhat later. Symptoms occurring days after a food is ingested are not likely related to the food.

When to call the doctor

Anaphylaxis is an extreme reaction to a food, usually peanuts or nuts. It causes swelling of the throat and bronchial passages, a drop in blood pressure, shock, and even death. A child with anaphylaxis should be taken to the emergency room immediately. If an emergency epinephrine pen is available, it should be administered immediately.

If a child experiences any type of allergy symptoms after eating, the child should be evaluated. Of particular concern are digestive symptoms that keep the child from eating properly or cause the child to lose weight. Equally important are neurological symptoms, especially headaches. Digestive and neurological symptoms could also be an indication of other underlying disorders. Therefore, the child should be seen by a doctor.

Diagnosis

Having a child evaluated as soon as possible will identify the offending food and allow parents to eliminate it from the child's diet. Many allergists, or doctors who specialize in allergies, will do a skin-prick test followed by a blood test. The skin-prick test is a series of pricks on the child's skin with a plastic applicator that contains a single food in concentrated form. A food allergy has been identified if the child's skin reacts by welting or becoming red. The skin-prick test for foods (not for aeroallergens) has a high incidence of false positives; that is, the test may be positive but the child is not truly allergic, or does not have symptoms from the food. This test is not used on a child with severe anaphylactic reactions or on children with widespread eczema, a skin disorder.

The allergist may also do a food challenge in the doctor's office. The child is fed the suspected food in increasing amounts to see what kind of reaction occurs.

One of the tests allergists use is called the RAST (Radio-Allergo-Sorbent Test). It measures the amount of IgE antibody in the blood that is produced for certain known food allergens. Like the skin-prick test, RAST and other antibody tests have a high rate of false positives.

Some doctors will put the child on an elimination diet for one week to 10 days. The basic elimination diet is a series of foods that have proven not to be allergy triggers. This diet consists of foods such as lamb, poultry, rice, vegetables, and all fruits, except citrus and berries. One new food is introduced each week. Parents record the child's reaction to each food. If the child has no reaction, the food is considered safe and can remain in the diet. If there is a reaction, it is noted and the food is removed. The child continues the elimination diet for a few more days, at which time another food is introduced. The elimination diet is often done after skin testing, so there is a logical guide for what to eliminate.

Treatment

The only treatment for IgE-mediated reactions to foods is avoidance. These reactions, as well as intolerances, are not responsive to desensitization. An epi-pen should be kept in the home for all IgE mediated food allergies and all inadvertent reactions should be treated.

It is not unusual for children to crave the very foods to which they are allergic. When the child is placed on an elimination diet, often the body will rebel at not being given the foods that cause it to react and will produce cravings for those foods.

Some doctors will prescribe antihistamines to help manage symptoms. These, however, are for use after an episode and not for an extended period.

Nutritional concerns

Eliminating one food or even one food family from a child's diet will not interfere with his or her nutritional needs, nor will it keep the child from growing properly. There is enough variety in the foods available in the American diet to meet any child's needs. Some foods, however, may be difficult to find sufficient replacements for if the child wants substitutes. Wheat is particularly difficult to replace, although bread, pasta, and pastry products made with oat and rice flours are good substitutes. However, they do not taste or look exactly like risen wheat bread or regular pasta.

Prognosis

Children are known to outgrow milk allergies in most cases, butfor safety purposesreintroduction in a medical setting is advised. Egg allergy disappearance is not as high as it is for milk allergy. Sensitivities to wheat and soy are also outgrown. Allergies to peanuts, shellfish, and other foods that can produce anaphylaxis usually remain with the child throughout life.

Prevention

If both parents have food allergies, precautions should be taken to minimize the risk of the child having a food allergy, too. Before birth and while breastfeeding, the mother can limit the baby's exposure to allergens by not bingeing on foods known to cause allergies. Breast-feeding delays the onset of allergies, but does not avoid them. The secretory IgA in breast milk fights infection but is not shown to avoid absorption of allergies.

Solid foods are slowly introduced at four to six months of age. The first solid foods should be those that have shown the potential for not producing an allergic reaction, such as fruits (except citrus fruits and berries), vegetables, and rice. Early introduction of highly allergenic foods may predispose a child to reactions, but this is controversial. It is recommended that parents avoid feeding the child highly allergenic foods until three years of age, if possible. The list of highly allergenic foods includes nuts, peanuts, fish, shellfish, and eggs. Whole cow's milknot cow's milk formulashould be avoided during the first year. Having the child eat a variety of foods will also keep the child from too much exposure to any one particular food family.

KEY TERMS

Allergen A foreign substance that provokes an immune reaction or allergic response in some sensitive people but not in most others.

Allergists Doctors who specialize in allergies.

Antibody A special protein made by the body's immune system as a defense against foreign material (bacteria, viruses, etc.) that enters the body. It is uniquely designed to attack and neutralize the specific antigen that triggered the immune response.

Cross-reaction A reaction that occurs in blood testing when a disease agent reacts to the specific antibody for another disease agent.

Histamine A substance released by immune system cells in response to the presence of an allergen. It stimulates widening of blood vessels and increased porousness of blood vessel walls so that fluid and protein leak out from the blood into the surrounding tissue, causing localised inflammation of the tissue.

Immunoglobulin G (IgG) Immunoglobulin type gamma, the most common type found in the blood and tissue fluids.

Lactose A sugar found in milk and milk products.

Parents should make sure that the baby's first foods and those during the first few years of life are pure, unprocessed foods. Packaged and prepared foods (soups, stews, and toddler dinners, for example) contain many foods mixed together, along with fillers, usually wheat products, and possibly flavorings, sugar, and salt. By feeding a toddler a piece of boneless chicken, some green peas, a few cooked carrots, and a bit of potato instead of a can of chicken stew, parents can identify exactly what foods the child is eating and in what quantities. Therefore, if there is an allergic reaction, it is easier to identify what triggered it.

Parental concerns

Because children can come into contact with food allergens at school and during extracurricular activities , parents should meet with school officials to discuss procedures for keeping their children safe. Parents and school personnel should develop an action plan for dealing with allergens in the school and handling an emergency. Not only should the cafeteria staff be notified about the food allergy, but parents should also ask about snack time, birthdays and holiday celebrations, field trips, and arts and crafts projects. Arrangements should be made to keep medications to treat accidental exposure at the school, and personnel should be trained in their use.

Due to the seriousness of nut allergies and other allergies that can cause anaphylaxis, some school districts have created policies that forbid nuts on school premises and do not allow students to trade food at lunch. Some parents have lobbied school boards for such restrictions.

Avoiding the trigger food may be very problematic, even at home. Parents need to become proficient label readers, especially if the allergen is a nut or other food that may cause anaphylaxis. Understanding what the ingredient names mean is critical to total food avoidance. For example, dairy products can be listed as milk, casein, whey, and sodium caseinate. If a child is allergic to corn, it can be found not only as corn and corn syrup, but also cornstarch, which is a binding agent in a number of medications, including acetaminophen (Tylenol). Consultation with a dietitian can help parents understand food labels.

Peanut allergies in the United States doubled between 1997 and 2002. A controversial British study, reported in 2003, found a peanut/soy link, which is clinically rare. The study reported a link between early use of soy formula and peanut oil baby lotion in the later diagnosis of peanut food allergy. Soy formula may sensitize an infant to legumes, and therefore to peanuts. Peanut oil, known by doctors and nurses as arachis oil, is found in baby lotion and creams, especially those used to treat diaper rash , eczema, and dry skin.

Children who have severe reactions to a trigger food should wear a medical alert bracelet. Parents should also have on hand an emergency epinephrine-filled syringe like those found in bee-sting kits, or an epinephrine pen.

Parents should also notify day-care providers, Girl Scout and Boy Scout leaders, religious education teachers, sports coaches, and parents of their child's friends. They should explain what foods their child is allergic to, how the child reacts to the food, and how adults can help, either by making sure these foods are not served as snacks or by giving emergency care or support during an allergic reaction. In addition, parents can teach their child how to ask for help.

See also Lactose intolerance.

Resources

BOOKS

Barber, Marianne S. The Parent's Guide to Food Allergies: Clear and Complete Advice from the Experts on Raising Your Food-Allergic Child. NY: Owl Books, 2001.

Coss, Linda Marienhoff. What's to Eat? The Milk-Free, Egg-Free, Nut-Free Food Allergy Cookbook. Lake Forest, CA: Plumtree Press, 2000.

Smith, Nicole S. Allie the Allergic Elephant: A Children's Story of Peanut Allergies. San Francisco: Jungle Communications, Inc., 2002.

Weiner, Ellen, and Moss Freedman. Taking Food Allergies to School. Plainville, NY: JayJo Books, 1999.

Young, Michael C. The Peanut Allergy Answer Book. Gloucester, MA: Fair Winds Press, 2001.

PERIODICALS

". . .And It's Easy to Misinterpret Correct Food Labels." Child Health Alert (Oct. 2002): 424.

"Origins of Peanut Allergy." Archives of Disease in Childhood. 88, no. 8 (August 2003): 694.

Vander Shaaf, Rachelle. "Is It a Food Allergy?" Parenting XVI, no. 5 (June 1, 2002): 38.

ORGANIZATIONS

Food Allergy & Anaphylaxis Network. 11781 Lee Jackson Hwy., Suite 160, Fairfax, VA 22033-3309. (800) 929-4040. Web site: </www.foodallergy.org>.

Janie Franz

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Franz, Janie. "Food Allergies and Sensitivities." Gale Encyclopedia of Children's Health: Infancy through Adolescence. 2006. Retrieved June 30, 2016 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3447200243.html

Allergies and Intolerances

Allergies and Intolerances

Food allergies affect approximately 3 percent of children and 1 percent of adults in the United States. It is estimated that an even larger percentage of the population experiences problems with food intolerance. Worldwide, adverse reactions to food constitute a significant public health issue.

Definitions

The term adverse reaction is used to describe health problems linked to food. Food allergy and food intolerance are two types of adverse food reactions (food-borne illnesses caused by bacterial, viral, or other forms of contamination are also adverse reactions). A food allergy is said to exist when the health problem is linked to a malfunction of the immune system . It is believed that this malfunctioning occurs when the body identifies a food protein (allergen ) as a harmful substance. Food intolerance occurs when the underlying problem causing the adverse reaction is not related to a malfunction of the immune system. One example of a food intolerance is lactose intolerance , a condition affecting people who cannot digest milk due to a deficiency of the enzyme lactase, which breaks down milk sugar (lactose).

Common Foods Associated with Food Allergy

Almost any food can cause an allergy, though the foods most commonly associated with an allergic reaction are those frequently consumed by a population. For example, an allergy to rice is common in Southeast Asia, while fish allergy is a problem in the Scandinavian countries, where fish is frequently consumed (even at breakfast). Age is also a factor influencing the types of foods to which a person might be allergic. In the United States, common foods to which adults are allergic include eggs, shrimp, lobster, peanuts, other nuts, and fish. U.S. children who have food allergies find their problems are most frequently linked to milk, soy, eggs, and peanuts. Infants may be allergic to cow's milk or soy formulas. Some food allergies may be outgrown, but allergies to peanuts, shrimp, and fish tend to last throughout life. In addition, some individuals are only allergic to one food, whereas some are allergic to several foods.

An allergic reaction can be triggered by a very small amount of a food. Persons with food allergies need to read food labels carefully and ask restaurant workers about food ingredients, and the food industry needs to ensure that processed foods are appropriately prepared so that people are not exposed to food allergens unknowingly. This may happen when improperly cleaned food equipment is used to prepare multiple types of food.

Food Allergy: Clinical Presentation and Diagnosis

Health problems associated with food allergies can involve the gastrointestinal system, the respiratory system , the skin, and the eyes. Persons with a food allergy may have difficulty breathing, or they may have problems with itching, rashes, swelling, nausea , or vomiting. A food allergy may also be a cause of asthma .

The symptoms of food allergy vary widely from person to person. Food allergies can also cause a severe clinical reaction known as anaphylaxis , which can result in death. Anaphylaxis may be characterized by throat and lip swelling, shortness of breath, sweating, itching, and feeling very faint.

Diagnosis of a food allergy usually involves a careful examination of the patient's symptom history. Other causes of symptoms must be ruled out, and in some instances the suspected food or foods will be eliminated from the diet to see if symptoms stop. Blood tests or skin tests may also be performed. One test sometimes used to diagnose food allergy is the double-blind, placebo-controlled food challenge. This test involves giving a patient a capsule containing a suspected food allergen and a capsule without the allergen (the placebo) and seeing if either causes symptoms in a controlled clinical setting. The test is called double-blind because neither the patient nor the physician evaluating the symptoms is aware of which capsule contains the allergen at the time the testing occurs.

Common Foods Associated with Intolerance

Foods associated with intolerance include: preserved foods, foods containing monosodium glutamate (MSG, a flavor enhancer), and specific foods such as milk, pickled herring, soy sauce, chili peppers, and nutmeg. Intolerance to lactose is a major problem for many populations. In the United States, lactose intolerance is common among those of African and Asian descent. The Native American population also has a high prevalence of lactose intolerance.

For many food intolerances, including those listed above, specific chemicals or enzyme abnormalities have been identified as being associated with the intolerance. Lactose intolerance is associated with problems with the enzyme lactase. Chemicals associated with food intolerance include sulfite (in preserved foods), tyramine (in pickled herring and soy sauce), capsaicin (in chili peppers), and myristicin (in nutmeg).

Food Intolerance: Clinical Presentation and Diagnosis

Health problems caused by food intolerance vary depending upon the food and chemical involved. The amount of a food eaten may also play a role. Lactose intolerance is usually characterized by gastrointestinal problems such as bloating and diarrhea. Sulfite intolerance is typically characterized by difficulty in breathing. Those sensitive to MSG may experience a variety of symptoms, such as headache, numbness, and rapid heartbeat. Tyramine, found in pickled herring, soy sauce, red wine, and other foods, has been linked to migraine headache. Capsaicin can cause a "burning" pain in the mouth and other problems, such as nausea and vomiting. Myristicin has been associated with anxiety , chest pressure, hallucinations, fever, and skin redness.

Diagnostic techniques for food intolerances vary depending upon the specific intolerance suspected. Symptom history and elimination diets are tools that are used, and the double-blind, placebo-controlled food challenge may also be helpful. Diagnosis of lactose intolerance in adults may involve measuring the blood to see if lactose is being broken down and showing up as blood sugar (glucose ), or by measuring the level of hydrogen in the breath, which is increased in persons who are lactose intolerant (lactose produces hydrogen gas in the colon).

Controversies Related to Food Allergies and Intolerances

Controversial issues in this area include the diagnosis of brain allergy , the diagnosis of environmental illness related to food allergy, and the diagnosis of yeast allergy . The connection of these problems to food allergies is not universally recognized. Some have also linked hyperactivity to food allergy or intolerance. Hyperactivity in children, in some instances, may be related to eating large amounts of food additives , but it is not accepted to be an allergic condition by the majority of the scientific community.

Other controversies relate to testing for food allergies. One controversial test is cytotoxic testing, which involves testing blood in the presence of the suspected food allergen to see if the blood cells are killed.

Peanut Allergies

Peanut allergies, which are among the most widespread food allergies, affect more than 1.5 million people in the United States. Symptoms of an allergic reaction may include a flushed face, hives, difficulty breathing or swallowing, vomiting, dizziness, chills, and loss of consciousness. The reaction of an allergic person to peanuts can be rapid and dramatic, sometimes causing death within minutes. The incidence of peanut allergies among children doubled in the United States between 1997 and 2002, prompting some schools to consider banning peanuts and peanut products from their premises. Proponents of a ban note that as little as half a peanut can be fatal in an allergic child, and that the risk of shared lunches or other accidental exposure is too great. Others argue that a peanut ban provides a false sense of security for children who inhabit a peanut-ridden world, and that educating students and school personnel about the problem, and preparing for the occasional incident, are more appropriate responses.

Paula Kepos

Treatment of Food Allergies and Intolerances

The major mode of treatment for food allergies and intolerances is for the person to avoid consuming the food or foods that seem to cause health problems. This involves a high degree of dietary awareness and careful food selection. When foods are eliminated from the diet, it is important to ensure the nutritional adequacy of the diet, and some individuals may need to take dietary supplements. There are some food intolerances, such as lactose intolerance, where individuals may be able to reduce the amount of the food consumed and not totally eliminate it from the diet. People with lactose intolerance do not have to completely eliminate milk products, though they must reduce their intake of lactose (milk sugar) to a manageable level.

see also Additives and Preservatives.

Judy E. Perkin

Bibliography

Koerner, Celide B., and Munoz-Furlong, Anne (1998). Food Allergies. Minneapolis, MN: Chronimed.

Metcalfe, Dean D.; Sampson, Hugh A.; and Simon, Richard A. (1997). Food Allergy: Adverse Reactions to Foods and Food Additives. Cambridge, MA: Blackwell Science.

Trevino, Richard J., and Dixon, Hamilton S., eds. (1997). Food Allergy. New York, NY: Thieme Medical.

Internet Resources

American Academy of Allergy, Asthma, and Immunology. "Media Resources: Position Statement 14." Available from <http://www.aaaai.org/media>

National Digestive Diseases Information Clearinghouse. "Lactose Intolerance." Available from <http://www.niddk.nih.gov>

National Institute of Allergy and Infectious Diseases, and the National Institutes of Health. "Food Allergy and Intolerances Fact Sheet." Available from <http://www.niaid.nih.gov>

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