I am currently 50 years old and diagnosed with CSID at the age of 3. I went through many yesrs of my mum trying to figure out what to feed me until I met with an awesome dietician at the age of 12. I now liveva relatively normal life and can eat most foods, some with more moderation than others.
The dietician eliminated all sucrose, starch and natural sugar from my diet for 2 weeks (HINT - glucose powder bought from a health food store can be substitute for sugar as it does not need to be broken down by the body).
After that I was given fact sheets (similar info is now available on the internet) detailing the amount of sucrose and starch in fruits, vegetables, grains, etc.
I then in 2 week intervals gradually intoduced small amounts until I found my tolerance levels.
Too much starch causes bloating/wind pains that will last up to 48 hours. Too much sucrose causes really bad stomach pains/cramps. Too much sugar causes diarrhea.
Diet is just s balancing act that becomes easier with practice.
I am happy to help out any people or parents navigste CSID.