Dietary tryptophane is metabolised by the gut microbiome to indole and IPA which reaches the human blood system. Indole is further metabolized into indoxyl sulfate which also reached the blood.d3fclassic metabolic pathwayPW:0000002Pathway Ontology19234110PubMedMetabolomics analysis reveals large effects of gut microflora on mammalian blood metabolites.Proc Natl Acad Sci U S A2009Wikoff WRAnfora ATLiu JSchultz PGLesley SAPeters ECSiuzdak G