About Food Allergies
While an estimated 40 to 50 million Americans have allergies, only 1 percent to 2 percent of all adults are allergic to foods or food additives. Eight percent of children under age 6 have adverse reactions to ingested foods; only 2 percent to 5 percent have confirmed food allergies. The following information addresses commonly asked questions regarding food allergy.
The most common symptoms of food allergy involve the skin and intestines. Skin rashes include hives and eczema. Intestinal symptoms typically include vomiting, nausea, stomach cramps, indigestion and diarrhea. Other symptoms can be asthma, with cough or wheezing; rhinitis, often including itchy, stuffy, runny nose and sneezing; and rarely, anaphylaxis, a severe allergic reaction that may be life threatening.
Because these symptoms can be caused by a number of different diseases other than food allergy, your allergist-immunologist may want to examine you to rule them out as the source of your problem.
In the individual with food allergy, the immune system produces increased amounts of immunoglobulin E antibody, or IgE. When these antibodies battle with food allergens, histamine and other chemicals are released as part of the body’s immune reaction to these substances. These chemicals can cause blood vessels to widen, smooth muscles to contract, and affected skin areas to become red, itchy and swollen. These IgE antibodies can be found in different body tissues – skin, intestines and lungs – where specific allergy symptoms, such as hives, vomiting, diarrhea and wheezing are observed.
Not all adverse reactions to foods are due to allergy. Some reactions to cow’s milk, for example, are related to a deficiency of an enzyme (lactase) that normally breaks down a sugar in milk (lactose). When individuals with lactase deficiency drink cow’s milk or eat other dairy products, they may experience intestinal symptoms, including stomach cramping, gas and diarrhea. This is sometimes misinterpreted as a food allergy.
Although food allergy occurs most often in infants and children, it can appear at any age and can be caused by foods that had been previously eaten without any problems. Finally, excessive exposure to a particular food may affect the overall rate of allergy to that food, as testified to by the high prevalence of fish allergy among Scandinavians and of rice allergy among the Japanese.
Keep in mind that, if you are allergic to a particular food, you might be allergic to related foods. For example, a person allergic to walnuts may also be allergic to pecans and persons allergic to shrimp may not tolerate crab and lobster. Likewise, a person allergic to peanuts may not tolerate one or two other members of the legume family, such as soy, peas or certain beans. Clinical research of individuals with food allergy, however, has demonstrated that the overwhelming majority of patients with food allergy are only allergic to one or two different foods. Complete restriction of all foods in one botanical family based on an allergy to one of its members is rarely necessary. Discuss these issues with your allergist.
If properly performed and interpreted, skin tests or IgE blood tests to foods are reliable and good screening tests for food allergy. However, it’s entirely possible to test “allergic” to a food (by skin testing or IgE blood testing) and yet have no symptoms when that food is eaten. Thus, confirmation requires appropriately designed oral challenge testing with each suspected food.
If only one or two foods seem to be causing allergic reactions, it may be necessary for the patient to go on a food elimination diet. The suspect food must be completely eliminated in any form for a short time – one to two weeks. If the allergic symptoms subside during abstinence and flare up when the food is ingested again, the likelihood of identifying the problem food can be increased.
If several foods appear to cause problems and/or the diagnosis of food allergy is equivocal, your allergist may want to confirm the role of each suspected food by oral food challenge testing. Not all positive skin tests and/or IgE blood tests equal a definite food allergy. With this in mind, food challenges are the best way to determine whether or not a food allergy really exists.
During an oral food challenge test the patient will eat or drink small portions of a suspected food in gradually increasing portions over a given period of time, usually under a physician’s supervision, to see if an allergic reaction occurs.
All patients with food allergies must make some changes in the foods they eat. Special food-allergy cookbooks, patient support groups and registered dietitians can provide valuable assistance regarding your diet. Your allergist can direct you to these resources.
Persons with histories of severe reactions need to be instructed in when and how to give themselves a shot of epinephrine (adrenaline) in the event of a severe allergic reaction. This medication is available in easy-to-use injectable devices and should be carried by persons with histories of severe allergic reactions. You should be taken to the hospital or call 911 and arrange for follow-up medical care for a severe reaction. Bracelets or necklaces may be worn to quickly alert medical personnel or other caretakers about food allergies.
After you have eliminated foods responsible for allergic reactions for a period of at least six months, your allergist may recommend that you undergo an oral food challenge under observation to reassess your symptoms. If you have no reaction and can ingest a normally prepared portion of the food, you will be able to safely reintroduce this food into your diet. If any symptoms of an allergic reaction do occur, the dietary restriction will need to be continued.
If you have had a severe immediate-type allergic reaction to a certain food, such as an anaphylactic reaction to peanuts, your allergist-immunologist may recommend that you never again eat this food and rarely would a food challenge be needed to confirm the history. Remember, in some very allergic persons a very small quantity of an allergenic food can produce a life-threatening reaction.
Patients who use caution and carefully follow an allergist’s advice can bring food allergy under control. Please contact your allergist-immunologist with further questions and concerns about food allergy.
There are other reactions to foods and these fall into the categories of non-immune and immune mediated reactions. Examples of immune mediated reactions include celiac disease, milk protein enterocolitis and Eosinophilic gastroenteritis while non-immune mediated reactions include lactose intolerance and food poisoning such as scromboid or staph toxins.
Peanut, treenuts, Milk, Egg, Soy, Wheat, Fish and Shellfish cause 85-90% of food allergic reactions.
- Timing- 90% of immediate type hypersensitivity reactions occur within 20-30 minutes of eating the food and the rest occur within 6 hours. Other food reactions take longer to occur hours to days.
- Reproducibility- All immunologic food reactions are reproducible. This is a great historical detail that adds credence to the mother’s concerns.
- Symptoms- Immediate food hypersensitivity affects many organ systems: skin, resp, gut, cardiac…other food reactions affect primarily the gut.
Food testing- many ways to get at food allergy. All are surrogates using biomarkers designed to avoid the gold standard ingestion challenge.
Testing- skin testing is the most accurate biomarker for food testing. It has a better negative predictive value than positive predictive value. That is, if the patient has a negative skin test for the food in question then there is a >95% likelihood they can eat it without an IgE mediated reaction. The positive predictive value is only 20-50% meaning that a positive test merely indicates sensitization and that there are false positives. The sensitivity of skin test for foods is >90% but the specificity is low at 50%
Patch testing has no value for immediate food allergy and is investigational only in delayed type food allergy testing.
Food specific IgG levels have no diagnostic or prognostic value and are positive in many patients that can eat the food with no problem. Provocation-neutralization, cytotoxicity testing and applied kinesiology (muscle strength testing) have no value in food allergy.
Single Blind Placebo Controlled Food Challenge
Open Food Challenge
Epinephrine is the only medication that can reverse or slow a food allergic reaction. It should be given within 5 minutes of a systemic reaction and the subject should go to the hospital.
Recent studies published in 2015 (LEAP study) and 2016 (EAT and LEAP-on) present evidence that early introduction (4-6 months of age) of foods associated with allergy may help prevent allergy to those foods, ie. cow’s milk, egg, peanut, tree nuts (almond, cashew, pistachio, walnut, pecan, hazelnut), soy, wheat, fish and shellfish.
If there is moderate to severe eczema or a history of an allergic reaction to any food, we recommend skin testing prior to the introduction of the allergenic foods listed above.
Allergenic foods should be introduced after other solid foods have been introduced and tolerated. If no reactions occur, a new allergenic food may be introduced every 3-5 days.
When introducing a food associated with allergy for the first time, given a very small amount first and wait 15 minutes. This should be done at home in the morning during a weekday during your doctor’s office hours. Then double the amount and advance as tolerated every 15 minutes. Nuts are a choking hazard in children less than 4 years old. Creamy nut butters or paste diluted in formula / breast milk and/or mixed with banana may be used for introduction in infants. Small amounts should be given rather than a large “glob”, which may also be a choking hazard. Bamba is a corn puff made with peanut butter, and it may be used in infants as well.
Ideally, once the food it tolerated, it should stay in the diet every week. ~7 gm of food protein is the goal per week (ie. 1 scrambled egg, 2 tablespoons of peanut butter or tree nut butter). Eating more than 7 gm is not a problem.
Dye and preservative allergy is rare <1%.
Carmine from the dried female insect Dactylopius coccus costa and Annatto from the seed of the tree Bixa orellana are rare but proven causes of IgE mediated reactions.
Red dye #40 and FD&C yellow #5 are common complaints but there have been only a handful of published proven reactions to these chemicals…so this is hype.