Ig G Food Sensitivity (or food intolerance) is a type IV delayed hypersensitivity reaction in the immune system that can occur a few hour and up 72 hours after ingestion of the reactive food. This window of time makes it difficult to link one’s symptom to the food eaten a day or two prior. Such hidden allergies are often the cause of many chronic symptoms. The immune response to delayed food reactions are often caused by antibodies other than Ig E. They are mediated by immunoglobulins: Ig G, Ig A, Ig M and Ig D. The Ig G antibody is the largest circulating antibody in our immune system (about 80-85% of our white blood cells) and can cross the placenta from mother to child. Ig G antibodies are the most common form of immunologic-mediated food responses. These antibodies combine with the food particles in the blood to form “immune complexes” which cause inflammatory reactions in tissues. Such inflammatory reactions can occur in any part of the body, thus producing many kinds of symptoms such as headache, eczema, joint pain, mental disorders, etc.