Gut & Microbiome
microbial tryptophan catabolites activate intestinal AhR
📅 Last reviewed: 2026-08-11 ⓘ
Evidence ladder
How far up the ladder this claim has climbed. A high consensus on a low rung means "consistent so far," not "proven in people."
Top evidence so far: Animal studies (Animal)
How the studies fall
What the evidence shows
Shared by H1 and H3, and the best-evidenced mechanism step in either. Gut bacteria convert dietary tryptophan into indole derivatives that are direct AhR ligands; this is replicated across independent disease models and, usefully for us, has been shown specifically for L. reuteri, the organism both hypotheses propose.
The evidence (4)
| Source | Grade | Stance | Quality | Finding |
|---|---|---|---|---|
| ? 2021 · Gut | animal | supports | moderate | Microbiota tryptophan metabolism induced AhR activation and improved alcoholic liver disease in mice; targeting the pathway reproduced the effect. |
| Zhang T 2025 · Diseases of the colon and rectum | in-vitro | supports | low | Tryptophan metabolites improved intestinal mucosal barrier function via AhR, adding an intestinal-epithelium locus for the same ligand-receptor step. |
| ? 2021 · Cellular and molecular life sciences : CMLS | animal | supports | moderate | Gut microbiota-derived tryptophan metabolism mediates renal fibrosis via the aryl hydrocarbon receptor, establishing the metabolite-to-receptor step in vivo. |
| Zhao C 2021 · PLoS pathogens | animal | supports | moderate | AhR activation by Limosilactobacillus reuteri tryptophan metabolism alleviated mastitis in mice — the specific organism proposed in H1 and H3 shown to generate AhR-activating tryptophan metabolites. |
Disagree, or know a study we missed?
We grade by evidence, not opinions. The way to weigh in is to point us to a study we haven't cited (check the evidence table above first), or to flag a problem with one we have. Every submission is reviewed; if it holds up, the grade updates and shows in Science Changes Its Mind.
Opens a short form. You'll sign in with Google so submissions are tied to a real account — we don't display your identity, and we only accept a link we can verify (PubMed, DOI, ClinicalTrials.gov).
Educational only, not medical advice. Grades and scores reflect published evidence weighted by study design and quality; see the methodology.