Gut & Microbiome

microbial tryptophan catabolites activates intestinal AhR

Leans support(Animal or laboratory evidence) Gut & Microbiome 🐭 Non-human evidence

RefutedContestedStrong support

consensus score 1.00

⚖️ Thin evidence — read the needle loosely. The score shows which way the studies lean, but there are too few independent, high-quality ones to place it firmly. Expect this to move as better evidence arrives.

Why the rating is limited: animal or laboratory evidence.

The studies that point for or against this claim are all animal or laboratory studies. They do not establish the claimed effect in people.

Before this limit: strong support. Final rating: leans support.

📅 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)

MechanismIn-vitroAnimalObservationalRCTMeta-analysis

How the studies fall

3 support 0 contradict 0 tested null 0 mixed · 3 sources, 3 independent groups

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
Wrzosek L, Ciocan D, Hugot C, Spatz M, Dupeux M, Houron C, Lievin-Le Moal V, Puchois V, Ferrere G, Trainel N, Mercier-Nomé F, Durand S, Kroemer G, Voican CS, Emond P, Straube M, Sokol H, Perlemuter G, Cassard AM 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, Yu Z, Xu Y, Zhao L, Zhu F, Zhou Y, Gu L, Gong J 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.
Liu JR, Miao H, Deng DQ, Vaziri ND, Li P, Zhao YY 2021 · Cellular and molecular life sciences : CMLS	animal	supports	moderate	Narrative review, not an experiment: 'In this review, we will elucidate the relationship between gut microbiota-derived uremic toxins by tryptophan metabolism and AHR activation in CKD'; states 'Tryptophan metabolites as ligands can activate AHR signaling'. The old extract's 'establishing the step in vivo' overstated it. Review — zero weight.
Zhao C, Hu X, Bao L, Wu K, Feng L, Qiu M, Hao H, Fu Y, Zhang N 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.

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Educational only, not medical advice. Grades and scores reflect published evidence weighted by study design and quality; see the methodology.