The microbiome is a posible factor. There are bacteria in our gut that protects us from bad stuff, but with could have a lack of those bacteria cause being born in cesary, antibiotics, stress, not getting enough sun and excersy. I would recommend you to search: seed and viome. You will learn with seed, but you could try viome and see if it works. The gluten reaction could be cause with that protein you are feeding bad stuff in your gut, or your lack of gut bacteria cant boost your immune system enough to get through digestion of the gluten. The gluten is not good for everyone, but some doesnt get the heavy syntoms because of his immune system could be better. Try to see all of this like the volume, there are all kind of levels, to low to high