I received this excellent question from a reader in the UK who is preparing to start the FODMAPS elimination diet. As she reviewed the list of allowed foods for the elimination phase of the diet, she saw several foods that have caused GI problems for her in the past.
Readers, I recommend you simply cross out all foods you know worsen your symptoms and do not eat them during the elimination phase of the diet. There are many kinds of adverse reactions to food, and intolerance to FODMAPS carbohydrates is just one. There could be a variety of other reasons why foods that don't contain FODMAPS could cause symptoms, such as food allergy or immune-mediated delayed hypersensitivity reactions.
Hopefully, if you experience improvement on the FODMAPS elimination diet, you will have dramatically fewer IBS symptoms within a week or two. This will make the foods you don't tolerate "pop out" at you when you do eat them, whether FODMAPS-containing or not. As long as you don't have an IgE allergy to your problem foods, there is no harm in testing them (eating them) at some later date. Maybe you'll find you can tolerate small portions of them if your diet isn't loaded with other symptom-provoking foods!
