This may sound ridiculous for people who are not a therapist but can work for many sufferers of food allergy. A friend can do it for you. If you know the origin of food allergy, then it is easy to find the cure. Your subconscious state definitely know what had happened that time and for sure that would be likely traumatic. Take for instance; let your friend start the procedure by snapping his/her fingers or clapping his/her hands. Whatever it is, there is something that was imprinted subconsciously and still operates presently. Again try to imagine eating the foods you are allergic to, extend your imagination until the food allergy symptoms appear, and then observe your feelings.