Allergies

Pediatric Food Allergies and Food Intolerance

What is an Allergy?

An allergy is a hypersensitivity to environmental substances such as dust, pollen, and certain foods. Allergic individuals experience adverse reactions that do not normally occur in a larger population exposed to similar amounts of the specific allergen. Allergic reactions can be either local or systemic inflammatory responses.

Local symptoms of an allergic reaction can include swelling of the nasal mucosa in the nose, redness and itching of the conjunctiva of the eyes; sneezing, wheezing, and difficulty in breathing (including asthma attacks); fullness, pain in the ears, or impaired hearing (due to blockage of Eustachian tubes); rashes such as eczema, hives, or contact dermatitis; and headaches from sinus pressure.

Systemic responses, or anaphylaxis, can affect multiple body systems, especially the respiratory, circulatory, and digestive systems. Severity is variable, and extreme reactions may require an injection of epinephrine. Anaphylaxis can appear to subside and then recur over a prolonged period of time.

There has been an apparent recent increase in the incidence of allergies of all kinds. Explanations include improved diagnosis; extensive use and distribution of chemicals in all aspects of modern life (multiple chemical sensitivity); imperfect distinctions between allergies, intolerance, and actual toxins; and the increased use of antibiotics and vaccinations in the treatment and prevention of diseases that may have unintended consequences for the human immune response.

Food Allergies

A food allergy is an immune system response to one’s diet. The body mistakes an ingredient in the food as harmful, and mounts a defense against it in the form of antibodies. Allergy symptoms develop as the antibodies battle the invading food. Common food allergies include peanuts, tree nuts, fish, shellfish, milk, eggs, soy, and wheat, affecting as much as 8% of children and 4% of adults.

Food allergies typically develop from a sensitivity to certain proteins. The first time a food containing a culprit protein is ingested, the immune system responds by creating specific antibodies (immunoglobulin E, or IgE). After sensitization, whenever the food containing the protein is eaten, IgE antibodies and other chemicals, including histamine, are released in an attempt to expel the invader. Histamine is a powerful chemical that can affect several body systems, not just the gastrointestinal tract. The amount of food necessary to trigger an allergic reaction varies among individuals.

Specific symptoms of a food allergy in an individual depend on where the histamine is released in the body. Reactions sometimes present a combination or sequence of symptoms as the food is eaten and proceeds through the digestive system.

Symptoms of a food allergy can range from mild to severe, and may include:

  • Nausea
  • Stomach pain
  • Diarrhea
  • Rash, hives, or itchy skin
  • Shortness of breath
  • Chest pain
  • Swelling of the airways
  • Anaphylaxis

Both children and adults are susceptible to food allergies. Food allergies often run in families, and while there is strong evidence that genetic predispositions exist, they do not tend to fall into simple (classic Mendelian) inheritance patterns. Both allergies and asthma are complex genetic disorders involving interactions of multiple genes, some contributing to disease development and some having actual protective value, with each gene having its own variable tendency for expression. Possible risk factors and protective factors related to one’s environment and lifestyle have also been suggested by research.

Food Intolerance

Food intolerance is a digestive system response rather than an immune system response. Something in a certain food irritates the digestive system, or the system is unable to properly digest or break down that food. As with allergies, the amount of food necessary to trigger symptoms of intolerance also varies among individuals.

Symptoms of food intolerance can also range from mild to severe, and may include:

  • Nausea
  • Stomach pain
  • Diarrhea
  • Gas, cramps, or bloating
  • Vomiting
  • Heartburn and reflux
  • Headaches
  • Irritability or nervousness

Food intolerance may result from a lack of the specific enzymes required to properly digest certain proteins, as in lactose intolerance. Intolerance in some individuals may also be a reaction to other chemical ingredients in food, such as additives to provide color, enhance taste, or protect against bacteria. Sulfites, both naturally occurring and added to prevent mold, are a source of intolerance for some individuals. Salicylates, a group of chemicals found naturally in fruits, vegetables, nuts, and juices, may be a source of intolerance, triggering symptoms in individuals who are also sensitive to aspirin.

It is important to note that any food consumed in excessive quantities may cause digestive symptoms indistinguishable from intolerance.

Allergies, Intolerance, and Food Refusal

If a child continues to ingest food to which they have an undiagnosed allergy, even without the more obvious symptoms or problems with nutrition, lesions or irritations can form in the digestive track, making eating a painful ordeal and establishing more general habits of refusal. Unidentified food intolerances can also result in acute or chronic problems with digestion and nutrition that may or may not be complicated or masked by habits of refusal.

Diagnosis and Testing

Some pediatric food allergies can remain undiagnosed for many months, causing worry for parents and health risks for infants and children. Blood or mucous in the stool, reflux, skin rashes, and other disturbing symptoms can be diagnosed as viruses or colic, but turn out to be milk or soy allergies. Identifying the underlying medical conditions that impact the treatment of eating disorders requires a detailed analysis of possible irritants or allergens, as well as coincident or subsequent adverse reactions, even if they are not initially suspected.

Testing for allergies is typically constrained by age-related patterns of sensitization. Sensitization to foods can occur in babies that are only a few weeks old, while it is unusual to develop sensitization to respiratory allergens before two or three years of age. In preschoolers, sensitization to indoor allergens (such as pets, dust, or mites) is more common than sensitization to outdoor allergens (such as pollen).

If a pediatric food allergy is suspected, a pediatrician or allergist will review the history and symptoms noted after ingestion and, if the reactions are consistent with a food allergy, will order or perform appropriate tests, of which there are several types (listed below).

Skin tests are simple and direct, with results available in minutes:

Prick tests – A small amount of a suspected allergen, or a battery of allergens in specifically labeled locations, is inserted under the skin. A hive, or redness and swelling, will form where there is a reaction to the specific allergen, and so one can generally obtain a quick positive or negative result for Immunoglobulin G (IgG).

Patch tests – The suspected irritant is applied to the skin topically and held in place with an adhesive patch. A sterile control patch is also applied to another location. If hives appear under the suspect patch, but not under the control patch, then the test is positive.

A skin test cannot predict what kind of reaction might occur upon ingestion of a food containing the allergen, but it can confirm an allergy suggested by the patient’s history of reactions to particular foods.

Blood tests, most commonly the radioallergosorbent test (RAST), can measure the actual amount of IgG antibodies in the bloodstream, which is then compared to predictive values for certain foods. Blood tests allow for hundreds of allergens to be screened from a single sample, and cover inhalants as well as food allergens. However, non-IgG-mediated allergies cannot be detected by this method. There is some dispute about the significance of blood tests for IgG antibodies, which may be implicated in delayed onset food allergies (associated with viruses, bacteria, and fungi), in contrast to the more common rapid onset of IgG allergies.

Skin tests may be quicker and more sensitive than blood tests, depending on technique, but blood tests are less likely than skin tests to be affected by certain medications or a pre-existing rash. Blood tests are preferred when the subject may have such a high sensitivity level that administration of a suspected allergen could have serious side effects.

Food challenge tests are administered under strict supervision in closely monitored environments, ideally as double-blind, placebo-controlled tests, in order to eliminate other factors such as food preparation techniques or psychological reactions to food recognition.

Elimination diet is the deliberate removal of specific suspect foods or ingredients from a child’s diet. If the symptoms clear up after a period of time, the pediatrician or allergist will direct a gradual reintroduction of the avoided foods or ingredients, one at a time. If symptoms return, a specific diagnosis can usually be confirmed. This can be repeated to narrow the range of culprit ingredients, one at a time. A dietitian can assist in planning menus to compensate for the absence of nutrients normally found in potential allergenic food(s).

Elimination diets and food challenge tests cannot be used if anaphylactic or other severe reactions are involved.

Other tests to determine the severity and extent of malnutrition, malabsorption, and systemic involvement can include:

  • Complete blood count (CBC) to look for anemia
  • Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to evaluate inflammation
  • Comprehensive metabolic panel (CMP) to determine electrolyte, protein, and calcium levels
  • Vitamin D, E, and B12 levels to measure possible vitamin deficiencies
  • Stool fat to evaluate malabsorption

Other tools for the diagnosis of gastrointestinal food hypersensitivity and more serious specific disease conditions include biopsy from upper endoscopy or lower endoscopy (colonoscopy).

Differential diagnosis is always an important step before more intrusive measures. Lactose intolerance and celiac disease are each well-known reactions to very specific proteins. Irritable bowel syndrome may be due to a food allergy, but is an important diagnosis for intolerance when no allergens can be identified.

Treatment and Resolution

The primary treatment for food allergies or food intolerance is avoidance of the foods, or the ingredients in foods, identified as allergens or as triggers of other adverse digestive reactions.

About 50% of children with allergies or sensitivities to milk, egg, soy, or wheat outgrow these by age six or older. Of those who don’t and who are still allergic by age 12, less than 8% will eventually outgrow it. Peanut and tree nut allergies are less likely to be outgrown. Those children who do outgrow a food allergy may eventually relapse if they do not consume the former allergen in some regular fashion.

Risks

Serious risks can be avoided by staying informed and educating an affected child as they grow and learn to cope with their food sensitivities, remaining watchful of diet and environmental triggers, and regularly consulting a pediatrician about the specific risks associated with a known food sensitivity. Modest precautions will normally suffice.

Even airborne food particles can trigger an allergic reaction. Somewhat like secondhand smoke, there may be harmful effects for people who aren’t directly ingesting it. Unlike secondhand smoke, which can hurt everybody, airborne food particles are a hazard for only a very small minority. An estimated 3% of elementary-school-age children and 2% of adults have food allergies, and the number who are radically sensitive is a mere fraction of even that relatively small population.

Acknowledging the risks posed to people with food allergies, many countries have instituted laws that require food products be labeled if they contain any major allergens or by-products of major allergens. In the United States, the Food Allergen Labeling and Consumer Protection Act of 2004 requires the disclosure in clear, plain language.

A Closer Look

Celiac Disease

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Celiac disease (CD), also called gluten-sensitive enteropathy (GSE), is an autoimmune disorder of the small intestine, and a specific form of gluten intolerance or sensitivity.  Symptoms can include chronic diarrhea, malnutrition, and fatigue, but these may be absent and other associated symptoms in other organ systems may be observed instead, such as dermatitis herpetiformis, which is an extremely itchy skin eruption.

The disease is caused by a reaction to certain gluten proteins (prolamins) found in wheat, barley, and rye. It occurs in genetically predisposed individuals whose enzyme tissue, transglutaminase, modifies the protein, causing an inflammatory reaction of the immune system. This damages the villi in the lining of the small intestine and interferes with the absorption of any nutrients, not just those in food containing gluten.

Research suggests that the timing of exposure to gluten in childhood may be a factor in developing celiac disease, but the results in infants exposed to wheat, barley, or rye at various ages are inconclusive. Breastfeeding until the introduction of gluten-containing grains does show a reduced risk of developing celiac disease in infants.

Diagnosing celiac disease starts with blood antibody tests to measure levels of anti-endomysium (EMA) and anti-tissue transglutaminase. However, positive results are only suggestive of the diagnosis, whereas if the results are negative, celiac disease can be ruled out. An endoscopic biopsy of the small intestine to check for damage of the villi is the only way to confirm celiac disease.

Only a small percentage of gluten-intolerant children and adults test positive for celiac disease. Non-celiac gluten sensitivity (NCGS) is much more common, affecting as many as one in seven. A gluten challenge diet may be administered months or years after diagnosis of celiac disease in infants, since features of celiac disease may be mimicked by other conditions such as secondary disaccharidase deficiency or milk intolerance.

The only known effective treatment for celiac disease is a lifelong gluten-free diet. Strict adherence to the diet allows the intestines to heal, and in a majority of individuals, leads to the resolution of all symptoms, although there may be a persistence of related symptoms suggestive of irritable bowel syndrome.

upper-jenjunal-mucosal-immunopathology

Food and Asthma

before and after asthma episode

Asthma results when environmental triggers cause swelling in the air passages and the lungs. Symptoms can include wheezing, shortness of breath, and coughing, with attacks normally triggered by particles in the air or sudden changes in air temperature. Although food-triggered asthma is unusual, food allergies can themselves affect asthma in a variety of ways, and may share similar symptoms. Food ingredients that may trigger an asthma attack include: chemical additives such as benzoates, sulfites, or gallates, and some coloring agents; naturally occurring yeasts and molds, such as in bread or cheese; dairy products, wheat, eggs, seafood, soy, and nuts.

Some foods can reduce the severity of an asthma attack by dilating air passages and thinning the mucus, promoting freer breathing. In this category, spicy or pungent foods like chili, hot mustard, garlic, and onions work by stimulating nerves and releasing fluid in the mouth, throat, and lungs. Some foods—such as onions, fatty fish (high in omega-3 fatty acids), and others high in vitamin C—also contain anti-inflammatory components that help clear the airways. Beverages containing caffeine may also provide relief. Of course, strong spices or stimulants are not recommended for infants or small children.

Children are more likely to outgrow asthma if their blood tests show fewer and fewer allergy markers as they get older. Only some have asthma that is triggered by allergies, and only some of those allergies may be from food. If a child needs daily asthma medication, it’s important for them to take it, but the long-term use of asthma drugs has no effect on outgrowing asthma. Even using inhaled steroids has no effect on the outgrowing of asthma. In fact, children are more likely to outgrow asthma by outgrowing an allergy if they do not improve with inhaled steroids. Since inhaled steroids reduce inflammation and sensitivity to allergy triggers, this is a sign that asthma may not have been caused by an allergy in the first place.

Lactose Intolerance

Intolerance to lactose in milk and other dairy products is a common diagnosis in children, and physiologically normal for most adults. Lactose is the main sugar in milk and the only significant sugar from animal origin. The intestinal enzyme lactase is required to digest lactose, acting to break the bond between galactose and glucose. Most humans, like most mammals, tend to lose the ability to produce lactase after infancy. Significant production of lactase ceases between the ages of two and five.

Symptoms of lactose intolerance are caused by enteral bacteria in the digestive tract metabolizing the relative abundance of unabsorbed lactose, drawing excess water into the intestines and producing gas by fermentation in the colon. This can result in stomach cramps, bloating, flatulence, and diarrhea.

A common tool for diagnosis is the hydrogen breath test, which checks for evidence of incomplete digestion before and after the ingestion of lactose. Biopsy from upper or lower endoscopy can test for the presence or absence of lactase.

The incomplete absorption of lactose in normal infants with regular feeding patterns is called “functional lactase deficiency,” common occurring in the first week of life and persisting for up to five months. Primary acquired lactase deficiency, more commonly referred to as lactase non-persistence (LNP), occurs after weaning from breast milk, and is very common in children who are up to six years of age. Secondary acquired lactase non-persistence is the result of damage to the mucosa of the small intestine, possibly from gastroenteritis, cow’s milk protein intolerance, or celiac disease. Congenital alactasia, or hypolactasia, is an extremely rare condition, found mainly in Scandinavia, in which affected infants do not gain weight and fail to thrive. Diagnosis must also distinguish lactose intolerance from a milk allergy (see below).

Milk Allergy

An allergic reaction to one or more proteins in milk can cause an infant to be fussy and irritable, with an upset stomach and other symptoms. Many children who are allergic to cow’s milk may also react to goat’s and sheep’s milk, and some may also be allergic to protein in soy milk. Infants who are breastfed are less likely to develop a milk allergy than infants who are formula-fed, but it is not clear why some develop a milk allergy and others do not. As with many allergies, there may be a genetic predisposition.

Symptoms of a milk allergy usually appear within the first few months of life. A slow-onset reaction is more common, occurring a week or so after consuming cow’s milk, and involves loose stools, vomiting, gagging, food refusal, colic, or rashes. Less common rapid-onset reactions come on suddenly after feeding, and involve vomiting, wheezing, swelling, or hives. Anaphylaxis can occur, but this potentially serious reaction is more common in other food allergies than in a milk allergy.

There is no single test to diagnose a milk allergy, and symptoms can be similar to lactose intolerance and other health conditions. A pediatrician may order a skin test in addition to a stool and blood test. Repetitive oral challenge tests are sometimes necessary to confirm a diagnosis.

If breastfeeding, treatment includes restricting dairy products in the mother’s diet, which should then be supplemented with alternative sources of calcium and other nutrients. If formula feeding, a pediatrician may advise a soy-based formula. If soy is not tolerated, then another hypoallergenic formula may be recommended. Goat’s milk, rice milk, and almond milk are not recommended for infants. Once the switch away from milk is made, symptoms should disappear within a few weeks. Most children outgrow a milk allergy by age two, but it can persist into adulthood.

Peanut and Tree Nut Allergies

An allergic reaction or hypersensitivity to a variety of dietary substances in peanuts can lead to a range of symptoms in as many as 1% of children and adults. Symptoms can include frequent urination, hypotension, hives, flushing, vomiting, itching, and bronchial constriction. The most severe cases result in anaphylaxis, which requires immediate medical attention and treatment with epinephrine. As with most allergies, avoidance and dietary exclusion is the only effective treatment, but around 25% of children with a peanut allergy grow out of it.

Tree nut allergies are distinct from peanut allergies in that they are caused by different foods with different allergenic components, and an allergy to one does not mean an allergy to the other, although they can both occur in the same individual. Symptoms of other nut allergies are very much the same as those of peanut allergies. Tree nut allergies occur mainly in children, may be less common than peanut allergies, and are usually also treated by exclusion and avoidance of suspect nuts, nut particles, and nut oils.

Eosinophilic Esophagitis

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Eosinophilic esophagitis (EE) is caused by the infiltration into the esophagus of a large number of eosinophils, a type of white blood cell, causing inflammation. Eosinophils are an important part of the immune system, helping resist certain types of infections, such as those caused by parasites. A variety of stimuli, including certain foods, may trigger abnormal production and an accumulation of eosinophils.

People with EE often have other allergic diseases such as asthma or eczema. EE can affect people of all ages, genders, and ethnic backgrounds. In some families, there may be an inherited tendency or genetic predisposition. EE is thought to be the most common type of eosinophil-associated gastrointestinal disorder.

The diagnosis of EE is often delayed, sometimes for years, because of a lack of awareness of the disorder and disagreement concerning specific diagnostic criteria, but the diagnosis can be confirmed with biopsies in the majority of cases. In rare cases, it may be difficult to distinguish eosinophilic esophagitis from gastroesophageal reflux disease (GERD).

Most children with EE respond favorably to dietary treatments. Dietary restrictions can be guided by food allergy testing and refined by food trials once the symptoms are resolved. Medications for EE most commonly include steroids to control inflammation and suppress the eosinophils, if dietary measures do not resolve the symptoms.

Links to Key Allergy Sites

Citations

  1. Metcalfe, Dean D., Hugh A. Sampson, and Ronald A. Simon, eds. 1997. Food Allergy: Adverse Reactions to Foods and Food Additives. 2nd ed. Cambridge, MA:Blackwell Science.
  2. Allergies and Intolerance in Children: www.ncbi.nlm.nih.gov.