The half-life of antibody producing lymphocytes is 5-6 weeks. IgG’s generally have a half life of 23 days. Therefore, it will take around 6-9 months to eliminate IgG antibodies when you strictly avoid the foods in question.
This depends on several factors:
the amount of IgG present (The higher the existing concentration, the longer it will take.) the strictness of avoidance possible cross reactivity to non-foods (Food can cross react with non-food items, such as pollen, viruses, and or dust mites. If such a cross reaction exists, it may take a very long time to eliminate the IgG’s or in some cases, they don’t disappear at all. This is mostly the case when you have never eaten the food before and still have antibodies present. Therefore, the antibody wasn’t triggered by the food, but by a non-food antigen of an unknown origin or which is ubiquitously present.)