@annpeters- As a new member, this site will not allow me to post links. In fact, it deleted my entire post because I included links to Foodmarble and Bella Lindemann's Functional Gut Health Clinic.

The Foodmarble is a breath tester that reports instant results, but I have never supplied any requested info on diet or bodily function, as I see that as somewhere between intrusive and creepy. Further, I don't put much faith in an algorithm for specific diagnosis. Also, be advised, the accuracy of this tester cannot be corroborated. OTOH, Johns Hopkins tested it a while back and gave it high marks.

Bella Lindemann seems to be extremely knowledgeable on these issues, but no longer advises individual clients. She has a blog as well as videos. But my experience with her assistant, Rachael Singh, was basically unhelpful, as she started each consult from scratch with no reference to prior discussions, and her advice, via email, consisted of generic copy/paste info that indicated to me that she had nothing specific to offer.