I am new to the Candida diet, but not to topics discussed often in Autism forums. One of these is gluten. You could get your son tested for a gluten sensitiviy. If that turns out to be a factor, there are grains that do not contain gluten. I too believe in the bible, and I believe that grain is the “staff of life”, but there are many grains that do not contain gluten (again, IF gluten is the problem, then those other grains could maybe help your little guy).
Some of the experts on here, like chris24, raster, or able could probably tell you which grains are gluten-free. Good luck!