Topics in Allergy
IgE & Non IgE Mediated Food Allergy & Elimination Diets
Food allergies may be of several types, each operating by its own mechanism, each quite different from the other in its characteristics. In addition, foods may cause problems for reasons other than allergy, an example being abdominal symptoms from milk in those who are lactose intolerant.
The main two types of food allergy are IGE MEDIATED FOOD ALLERGY and NON IGE MEDIATED FOOD ALLERGY.
IGE MEDIATED FOOD ALLERGY involves production of IgE antibody that attaches to mast cells and recognizes the structure of a food (allergen). When the food is eaten, it attaches to the IgE antibody causing the mast cell to release many materials that cause allergic symptoms. Allergy skin tests and RAST tests (if done correctly) accurately show if you produce IgE against the food allergen. This is the same mechanism involved in inhalant allergies and bee sting allergies. The characteristics of this type of allergy are:
***the reactions are usually sudden.
***they may be severe and even life threatening.
***small amounts of food may cause a reaction.
***they tend to be a lifelong problem.
For some foods (peanuts, shellfish) a positive skin test or RAST test indicated a high likelihood (over 90% chance) the food will cause problems when ingested-For more information on RAST testing for foods see: Interpreting RAST (Blood Test) Results For Food Allergies. For other foods (wheat, corn, some vegetables, etc) a positive test indicates a much lower likelihood of a reaction if eaten. Elimination and rechallenge with the food may be needed to determine the significance of the test result. DO NOT RECHALLENGE with a skin test or RAST test positive food or with any food you suspect caused immediate or severe symptoms without discussing this with us first. Some rechallenges may be very dangerous.
NON IGE MEDIATED FOOD ALLERGIES are quite different. We do not know the mechanism. IgE is clearly not involved and neither skin tests nor RAST tests help diagnose this type of allergy. Many other tests are touted by some to diagnose this form of food allergy. All have been proven to be worthless. The only way to assess non IgE mediated food allergy is by elimination and rechallenge trial. This is not as difficult as with IgE food allergies because only large amounts of food will provoke symptoms and food challenges do not have the risk of provoking severe reactions. The characteristics of non IgE mediated food allergies are:
***they are usually delayed with onset several hours (but not days) after ingestion.
***they may cause annoying symptoms but do not cause severe or life threating symptoms.
***larger amounts of food are required to cause a reaction. Trace amounts are not a problem.
***they are often transient, disappearing in several years.
ELIMINATION AND RECHALLENGE PROCEDURE:
1. For each food you suspect may have caused a non IgE mediated food allergy symptom you may do an elimination & rechallenge trial to determine if the food caused the symptom. NEVER RECHALLENGE with a skin test or RAST test positive food or with any food you suspect caused immediate or severe symptoms without discussing this with us first. Some rechallenges may be very dangerous.
***ELIMINATE the food as much as possible for 7 days (do not worry about trace amounts especially in NON IGE FOOD ALLERGY).
***Then CHALLENGE with 2-3 servings daily for 2 days.
2. If there is no reaction to the challenge you may leave the food in your diet.
3. If you do react to the challenge repeat the elimination and challenge 2 more time to be certain it was not coincidental.
NOTES REGARDING FOOD GROUPS:
MILK-eliminate the following foods as much as possible for 7 days, then challenge with 2-3 servings daily for 2 days:
***All forms of milk (whole, 2%, skim, goats milk, dried or powdered milk, evaporated milk, etc.).
***All forms of cheese and cottage cheese.
***All forms of ice cream, sherbets, yogurt.
***Foods with powdered milk such as some instant drinks, pancake mixes, etc.
You do not have to worry about small amounts of milk solids in baked goods, hotdogs, etc.
Use a milk free margarine.
Non dairy desert toppings may be used but avoid products that contain casein or whey.
Mocha Mix is a convenient substitute for milk and is found in most grocery stores.
2. WHEAT-eliminate all grains except rice and corn as much as possible for 7 days, then challenge with 2-3 servings daily for 2 days, remembering pasta is made from wheat.
3. CORN-do not worry about corn oil, corn syrup, corn starch, etc. It is mainly the protein in corn (whole corn, corn cereals, corn bread, etc.) that causes allergic reactions.
Eliminate all other sources of corn as much as possible for 7 days, then challenge with 2-3 servings daily for 2 days
4. LEGUMES-eliminate beans, peas, soy, and peanuts as much as possible for 7 days, then challenge with 2-3 servings daily for 2 days. You only need to rechallenge with legumes you suspect cause a problem or that are usually part of your diet. DO NOT CHALLENGE WITH PEANUT IF YOU HAVE HAD ANY SUGGESTION OF IMMEDIATE REACTION WITHOUT FIRST DISCUSSING THIS WITH US.
5. With most other foods you may eliminate only the food in question or seemingly close relatives (such as citrus if you suspect orange) as much as possible for 7 days, then challenge with 2-3 servings daily for 2 days with just the food in question. Ignore tables in books that talk about food families. These do not accurately describe allergic relationships.
The FOOD ALLERGY NETWORK has additional and frequently updated information about food allergies.
Food Allergy Network
10400 Eaton Place, Suite 107
Fairfax, VA 22030-3179
703.691.3179 Fax 703.691.2713
Another general allergy web site that has food allergy information and additional links is the American Academy of Allergy Asthma & Immunology: http://aaaai.org