Food Allergy and Food Intolerance Tests
Despite the first documented case of food allergy to cooked food back in 1921 (by Prausnitz and Kustner), all commercial food antigens, which are used to test for food allergy, are prepared from raw food. Most tests for IgE (allergy) and IgG (food intolerance) reactions are also measured against raw food.
Processing a food can cause alterations to the chemical make-up of the food. For example, processing may destroy existing epitopes on a protein or may cause new ones to be formed (neoallergen formation).
Neoallergen formation may explain why some individuals can tolerate a raw food but react to the food when it is processed. Studies have found neoallergens from pecans, cashew nut, walnut, wheat flour, egg, lentil, soybean, shrimp, tuna, apple, milk, plum, and potato.
The way a food is processed may also have an impact on the type of changes. The processing methods that may bring about changes include:
- Dry heat such as oven roasting.
- Wet heat such as boiling, blanching, and steaming.
- Non heat methods such as soaking, milling, fermentation, and dehusking.
A study carried out by Vojdani looked at both IgE and non IgE reactions against both raw and processed foods. Blood samples were obtained from 40 allergic individuals and 40 non-allergic individuals. The samples were tested against a range of raw and processed foods such as raw pork and bacon, raw tuna and canned tuna.
26 of the 40 samples from allergic individuals and 3 from the non allergic showed IgE antibodies against 5 or more food antigens.
These 29 samples were further tested: 20 showed very similar IgE antibody levels against raw and processed foods but 9 showed a 3-8 fold increase in IgE antibodies against processed foods as compared to raw food. For example, peanut butter was higher than raw peanut, cooked salmon was higher than raw salmon, boiled egg was higher than raw egg.
Further tests were carried out to measure IgG, IgA and IgM specific antibodies. These were higher in the group with identified allergies and the results were higher for processed foods than for raw foods.
Vojdani argues that one of the reasons traditional food sensitivity testing fails is that it does not reflect a real world non raw food diet.
The problem is not only that a food can change when processed but that the affect it has in the body can also be different when it is combined with other foods. So, a person “who is allergic to ketchup may not have an immune reaction to raw tomato”. Normal testing methods would not identify or resolve that person’s problems.
“These results confirm an earlier study that reported a case of food allergy to a wheat isolate used in sausage and pork pie, but without any allergic reaction to native wheat flour. This allergic reaction to wheat isolates was attributed to the induction of cryptic allergenic or the formation of new allergenic epitopes by technological and chemical processes.” [The study this refers to is: Leduc V, Moneret-Vautrin DA, Guerin L, Morisset M, Kanny G. Anaphylaxis to wheat isolates: immunochemical study of a case proved by means of double-blind, placebo-controlled food challenge. J Allergy Clin Immunol. 2003 Apr;111(4):897-9.]
Vojdani concludes that measuring food allergy and sensitivity could be improved if tests extended to include IgG, IgA and IgM as well as IgE and also used both raw and processed antigens.
My Comment
I fully agree that the use of just raw food in food allergy and food intolerance testing really does not make sense and is the cause of many people continuing to have problems with food after being told they do not have an allergy.
The use of tests to measure non-allergic food intolerance, such as IgG, is still a very contentious area. There really need to be more studies that try identify whether measuring these non IgE aspects tell us anything about food sensitivity or simply about what a person has eaten a great deal of lately.
For more information see my article on Food Intolerance testing.
REFERENCES
Vojdani A.
Detection of IgE, IgG, IgA and IgM antibodies against raw and processed food antigens.
Nutr Metab (Lond). 2009 May 12;6:22.