Perhaps glutamine. I have used it during healing of gluten-intolerance induce candida and leaky gut, and it worked pretty fast. I now use it for a few days to a week whenever I accidentally ingest gluten to help heal my gut and stop the contact pain I get when I eat after exposure. It has really helped me. I suppose if you are looking for true natural, you may want to see which foods contain the most glutamine and eat more of them.