Adverse Food Reactions: When is it an allergy?
To Your Health -- CHRC Newsletter
Winter 2002
By Kristina Hoffman Philpott, M.D., PAMF Allergy & Immunology
Unpleasant reactions to food affect most people at some time in their lives. One out of three people, when asked, may say they or a family member have a food allergy. However, in large medical studies, only about 3% of infants and toddlers have clinically proven food allergy, and in adults, this number drops to less than 1%. Why the difference between public perception and clinically proven prevalence? The main reason is because of the high prevalence of "food intolerances", which often are referred to incorrectly as "food allergies". A true food allergy, or hypersensitivity, is an abnormal response to a food that is triggered by the immune system. The immune system is a vast complex of many types of cells, antibodies, and molecular "messengers" which operate on many levels to keep the body safe from infections, among other functions. The immune system's components must be able to distinguish the difference between tiny foreign invaders and harmless proteins which are simply 'passing through'. When a part of the immune system overreacts to a food protein, an allergic reaction may result. Food intolerances differ from food allergies in that food intolerances do not involve the immune system. For those who have true food allergies, it is important to identify them and prevent reactions, because these reactions can be severe and potentially life-threatening.
Food Allergies
The main type of food allergy involves antibodies in the immune system known as immunoglobulin E (IgE). The 'allergic pathway' stimulated by IgE antibodies to specific foods, results in itching, hives, angioedema (localized tissue swelling in the skin, mouth, airway, and/or gut lining), wheezing, airway spasm, vomiting, and/or anaphylactic shock (the most severe form of an allergic reaction), occurring within a few minutes to hours after ingesting the causative food.
Atopic dermatitis (eczema) in infants and toddlers may be another symptom of food allergy. In recent medical studies, food allergy was a causative factor in almost half of children under the age of two years with moderate to severe atopic dermatitis. In older children or adults, food allergy is usually not a causative factor in atopic dermatitis.
There are some immune-mediated reactions to food proteins, which do not involve IgE antibody, but involve other mediators of the immune system. Milk- and/or soy-protein-induced enterocolitis syndrome in infants or toddlers is a primary example. The old name for this condition was "milk-protein intolerance" (not to be confused with "lactose intolerance").
Typically infants with this condition may have a combination of symptoms such as vomiting, colic, diarrhea, poor weight gain, or may even have blood in their stool. This is a different type of reaction than in infants who have hives or wheezing in reaction to milk or soy. In either condition, strict avoidance of milk and soy proteins for several months or longer usually results in eventual resolution for the affected child.
In children in the United States, the most common food allergens are milk, egg, peanut, soybean, wheat, and fish. In adults with food allergies, the most common culprits are shellfish (shrimp, escargot, squid, crab, clams, etc.), peanuts, tree nuts (walnuts, pine nuts, almonds, etc), fish, and egg. The food proteins (or allergens) responsible for this type of reaction are usually not broken down by cooking or by digestive enzymes. There is no significant difference in intestinal absorption of these proteins between allergic and non-allergic individuals. The difference lies with the individual's immune system's ability to develop 'tolerance' to these allergens, or not (in other words, to ignore the allergens or to react to them).
Food Intolerances
Most adverse food reactions fall into the category of food intolerances and not food allergies. A food intolerance can occur due to a direct physiologic effect of the food in susceptible individuals, but components of the immune system are not involved in causing the reaction. The most common food intolerance occurs in individuals with lactase deficiency, also known as 'lactose intolerance'. Lactase is an enzyme that is made by the cells lining the gut, and is responsible for breaking down lactose, the simple sugar found in dairy products. If an individual does not have the ability to make enough lactase, then the lactose is used by the bacteria in the gut, forming gas and leading to bloating, abdominal pain, and sometimes diarrhea. The terms 'lactose intolerance' and 'milk allergy' are completely different conditions with different medical treatments.
Some food intolerances are fairly obvious, such as spicy foods causing heartburn and a runny nose, or high-fat foods taking longer to digest and causing stomach cramps. A lesser-known food intolerance involves reactions that occur after individuals ingest certain foods that naturally contain 'histamine-like' substances, which can cause itching and hives. These symptoms can often be indistinguishable from a food allergic reaction. The foods typically implicated in this type of a reaction are certain types of cheeses, some wines, and some fish (like fresh tuna). Some patients who are prone to migraines are susceptible to this type of food intolerance.
Diagnosis
In order for physicians to help their patients distinguish a food allergy from food intolerance, it is helpful if the patient or the parent of the patient has kept a diet diary, in order to answer the following questions about past reactions:
- How long after ingestion of the specific food did symptoms begin to occur?
- How much of the food was ingested or contacted?
- Was this the first exposure to the food, and has it been eaten again since the time of the first reaction? (If so, did similar symptoms occur?)
- What were the symptoms, and in what sequence did they
occur? - How long did the symptoms last?
- What treatment, actions, or medicines were given? Did they help?
- Did anyone else have symptoms after the same meal?
- How was the food prepared?
- What other foods were ingested just prior to the allergic
reaction? - If the reaction occurred in a breastfeeding infant, what foods are in his/her mother's diet?
- How long has it been since the time of the last reaction?
- Has the suspected food been strictly eliminated from the diet? (i.e. even tiny amounts of the suspected food allergen contained in processed foods or cross-contaminated restaurant food?)
Sometimes a detailed history and dietary avoidance may not be enough to pinpoint the diagnosis. Elimination diets, if not monitored by a physician and/or dietitian, may be fraught with adverse nutritional, social, and psychological consequences. Further diagnostic tests and/or referral to an allergist or gastroenterologist may be indicated, depending upon the clinical history.
If the patient's clinical and dietary history suggest a food allergy and not a food intolerance, then a primary physician may recommend a consultation with an allergy specialist. After a thorough review of the history of the symptoms and a physical examination, an allergist may recommend allergy testing, usually an allergy prick-skin-test to check for allergic reactivity to the implicated food(s), or a blood test to measure the specific-IgE level to the implicated food. The allergist will interpret the results based on close correlation with the clinical history, and determine the next diagnostic step or treatment plan.
Treatment
Food allergies and food intolerances are treated by dietary avoidance of the causative food(s), with adequate nutritionally-equivalent alternatives substituted in the diet. Individuals with IgE-mediated food allergies have the potential to have a severe allergic reaction within minutes of even a tiny exposure to the food allergen. Once the food allergens have been identified, they need to be strictly avoided (which is not as easy as it sounds). Although the FDA requires food manufacturers and distributors to include ingredients on the label, the names used in labeling may not be an obvious indicator of the food allergen's presence. For example, a food may be called "nondairy" because it does not contain lactose, but the ingredients may include calcium "caseinate", which is a milk protein and is likely to cause a reaction in milk-allergic individuals (but not lactose-intolerant people). Additionally, some foods contain "undeclared" ingredients, which may be allergenic, but are not listed on the ingredient label. "Cross-contamination" at the food manufacturing location occurs when the same processing line is used for different food products, and tiny amounts of food proteins from one product end up in another product's package. Cross-contamination can occur in restaurants or at home in the kitchen, when food-preparation surfaces, pans, dishes, or utensils are used interchangeably when preparing different foods (for example, the peanut-butter knife in the jelly jar).
Avoiding allergenic foods requires time and vigilance, and can interfere with normal social activities (eating cookies at daycare or having dinner with friends or relatives becomes a minefield of potential reactions). Nutritionally-equivalent alternatives for the eliminated food(s) may be challenging to find. Breastfeeding mothers of allergic infants should avoid the allergenic food in their own as well as their child's diet. In highly allergenic patients, they may even react to inhaling cooking fumes (e.g. boiling shrimp) or aerosolized food particulates (e.g. peanut packages being opened nearby inside an airplane), or even by touching spilled food
residues.
Sometimes well-meaning relatives, friends, or even medical personnel, might encourage parents to give their food-allergic child tiny amounts of the food allergen on a regular basis to help them "get used to" the food or "tolerize" them to the food. This is not only a dangerous practice because of the risk of a severe allergic reaction, it also may prolong the allergy in the child, and delay the age when the child might actually "outgrow" the food allergy.
Even in the most careful families, accidental ingestions or contact may occur, and an allergic reaction may ensue within minutes. In patients with this type of food allergy, physicians usually prescribe an injectable epinephrine device, which is a life-saving medication (the same device which bee-sting allergic individuals carry with them). When used early in an allergic reaction, the epinephrine will almost always stop the reaction from progressing to a potentially life-threatening event. Antihistamines alone might stop the itching or the hives, but it is unlikely they will prevent respiratory distress or anaphylaxis. Food-allergic children in daycare or school should have a food allergy emergency action plan in place at the school. Additionally adult caregivers or teachers should be trained on recognizing early warning symptoms of an allergic reaction, and know how to use the injectable epinephrine device.
If carrying an injectable epinephrine device and/or asthma inhaler on board an airplane, be sure to obtain a letter in advance from your doctor. Increased airport security measures have caused some allergic travelers to be asked to present a letter explaining the medical necessity of these devices in their carry-on luggage. Also, if you or your children are peanut-allergic, be sure to call the airline several days before your departure date and request a peanut-free-zone on your flight.
Prognosis
In children with allergies to foods such as milk, soy, or egg, the prognosis is excellent, with resolution in 85% of children by 3 years of age. Strict avoidance of the food protein (even tiny 'hidden' amounts) is associated with resolution at a younger age than in children whose diets are not restricted completely. Deciding the age at which to re-introduce the food allergen to check for resolution (which means a scheduled oral food challenge under observation in a medical setting, for most children), depends upon the age of the child, clinical history, and the food in question. Unfortunately peanut, tree nut, shellfish, and fish allergy do not have the same resolution rate as with many other food allergies, and usually persist into adulthood. Therefore, food challenges, even in medical settings, are rarely done for these foods.
Prevention
Food allergies can be prevented or at least delayed in infants born into allergy-prone families. ("Allergy-prone" families include families who already have an allergic child, or if one or both parents have any type of allergic condition, like asthma, hay fever, atopic dermatitis, or food allergies). Breastfeeding for at least 6 months, if possible, is recommended with maternal avoidance of foods containing peanuts, nuts, egg, or seafood. If milk is eliminated from the mother's diet, alternative sources of calcium should be maintained. Milk or milk-based formulas should not be introduced into the infant's diet until after one year of age. Eggs should not be introduced until after age two. Exposure to peanut, tree nuts, and seafood should be delayed until after age six. There is no definitive medical evidence demonstrating that babies can be sensitized to specific foods prior to birth, but some allergy-prone pregnant women are avoiding peanuts and nuts in the last trimester as a precaution.
Summary
Food allergies are caused by immunologic reactions, which can result in a variety of skin, respiratory, gastrointestinal, and/or systemic manifestations. A complete clinical history and medical evaluation are the important initial steps in proper management of food allergies. Allergic individuals should become knowledgeable about their allergies, and work with their physicians in following an appropriate long-term treatment plan.
Further Resources
The Food Allergy Network has practical information on relevant topics like grocery shopping, reading ingredient lists for "tricky" labeling, avoiding food allergens at school, skin care for atopic dermatitis, alerts for product recalls because of undeclared food allergens, and many other valuable topics: Food Allergy & Anaphylaxis Network (1-800-929-4040; www.foodallergy.org). National Institutes of Health (NIH): Food Allergy -- An Overview.