Thank you for your inquiry.
Before I speak directly to your questions, it is important that you understand a blood test only indicates the presence of sensitization or IgE (the allergic antibody) against the allergen tested. It does not necessarily mean that that patient is allergic to the substance and will react to it. There are many people who have positive tests to foods who can eat those foods without a problem. There are a number of different reasons for this, but it is not necessary in many instances to restrict a food from the diet only because there is a positive blood test to the food. If a patient has eaten that food without difficulty, one would consider this test a measurement of sensitization (that is, exposure with a normal immune response) rather than allergy per se. Allergy to a food can only be definitively diagnosed by oral challenge.
Having said that, it is very clear that allergic reactions to soy sauce and corn oil, if they do occur, are extremely rare. I was not able to find, on a literature search, any documented anaphylaxis to either corn oil or soy sauce. So, in general, it appears safe for people who are actually allergic to both soy and corn to eat these products. Nonetheless, we cannot give you a definitive answer because of the complexity of the issue.
First of all, the amount of residual allergen in soy sauce, as within any oil or sauce, depends on the production process employed for that particular product. To illustrate that point, I have copied below an abstract regarding allergens in soy sauce. As you can see, the allergenicity can vary from brand to brand.
The same principle holds true for allergies to oil. I could find no study on corn oil per se, but, just to illustrate the point, I have copied below an abstract using nut oils to illustrate the point that there can be great variation in the content of allergen between products.
Having said this, again, in my experience, and according to a search of the literature, allergies to both soy sauce and corn oil are extremely rare. In general, it is safe for patients to eat these products even if they do have allergy to the native substance, but caution still applies based on the information gleaned from the abstracts copied below. Thus, there is still some controversy over this issue, and different allergists may recommend different strategies of avoidance to their patients. In general, I do not restrict corn oil, and would only rarely suggest restriction of soy sauce, and that is if a patient had experienced a severe reaction to soy.
Thank you again for your inquiry and we hope this response is helpful to you.
Soy sauce retains allergenicity through the fermentation/production process
The Journal of Allergy and Clinical Immunology
Volume 115, Issue 2, Supplement , Page S32, February 2005
Rationale: Soy allergy is one of the most prominent allergies in the worldwide population. The vast majority of soy sauces are produced through the fermentation of soy and wheat. Some soy sauce manufacturers tell finished food product processors (and also soy-and wheat-allergic patients who contact them) that the fermentation process destroys the allergenicity of their soy and wheat fermentation ingredients. This has not been proven to be the case by scientific experimentation, so the risk of reaction from soy sauce ingestion among soy-allergic and wheat-allergic/celiac patients is unknown.
Methods: Ten soy sauces were evaluated using three soy-specific animal IgG-based ELISAS (two of which are commercially available), by soy polymerase chain reaction (PCR) analysis, and also by RAST inhibition using sera from soy-allergic subjects.
Results: The soy IgG-based ELISA tests and PCR tests showed no detectable residues of soy protein or soy DNA in the ten sauces. However, in RAST inhibition (using soy flour as the solid phase), some soy sauces contained 10-30% residual activity.
Conclusions: Soy sauces made by fermentation of soy protein can retain some of their soy allergenicity (10-30% that of soy flour) through the fermentation/production process. Soy IgG-ELISA and PCR analyses do not detect the remaining allergenic residues in soy sauce. Therefore, results from these types of tests should not be used by soy sauce suppliers nor finished food manufacturers to indicate that soy sauce is devoid of allergenic residues and safe for soy-allergic individuals to consume. Soy-allergic patients should continue to be counseled to avoid soy sauce.
Journal of Allergy and Clinical Immunology
Volume 99, Issue 4, April 1997, Pages 502–507
Abstract Background: No information is available on allergenicity of tree nut oils, and information on peanut oils has been conflicting. Many of the nut oils now on the market undergo minimal processing and may contain residual antigen. Objective: This study was carried out to determine whether several of the new “gourmet” tree nut oils, as well as peanut oils, contain residual proteins that could bind IgE from sera of patients with allergy. Methods: Several brands of walnut, almond, hazelnut, pistachio, and macadamia nut oils were examined. Peanut oils, both unrefined oils (which have been shown to contain allergenic proteins) and refined oils (without previously demonstrable allergens), were also examined to confirm reproducibility of immunoreactivity as reported by other investigators. Oils were extracted with 0.2 mol/L ammonium bicarbonate, and protein concentrations in the aqueous extracts were measured. IgE binding was assayed by slot-blot and Western immunoblotting. Pooled sera from patients with a history of systemic reactions to various tree nuts or peanuts were used as appropriate. Results: The oil extracts known to be from oils that had undergone less processing at lower temperatures tended to demonstrate qualitatively greater IgE binding and higher protein concentrations. Conclusion: Tree nut and peanut oils may pose a threat to patients with allergy, depending on the method of manufacture and processing. (J Allergy Clin Immunol 1997;99:502-6).
Phil Lieberman, M.D.