The evidence on 3-indolepropionic acid and metabolic health, sorted honestly

Characterises the Clostridium sporogenes fld gene cluster (fldA/fldL, fldI, fldB/fldC, fldH; locus tags CLOSPO_00309–00311) converting tryptophan (and phenylalanine/tyrosine) into nine circulating aromatic-amino-acid metabolites including 3-indolepropionate. Mutating fldC abolishes 3-IPA production.

C. sporogenes uses reductive Stickland metabolism of amino acids, including the aromatic-amino-acid branch, to generate ATP — linking 3-IPA production to the organism's core energy metabolism rather than a side reaction.

3-IPA is a pregnane X receptor (PXR) ligand. In PXR-knockout (Nr1i2^-/-) and Nr1i2^-/-Tlr4^-/- mice, 3-IPA downregulates enterocyte TNF-alpha and upregulates junctional-protein mRNAs, strengthening intestinal barrier function.

3-IPA "partially activates" the aryl hydrocarbon receptor (AhR) to promote macrophage phagocytosis and attenuate septic injury in a mouse sepsis model.

3-IPA activates both AhR and PXR receptors and induces cytostatic effects plus oxidative stress in breast-cancer cell lines. An oncology in-vitro context, not a diabetes/metabolic finding.

3-IPA reduces activation markers in hepatic stellate cells in vitro, alongside the human cohort finding listed under Tier 4 below.

Germ-free mice produce no detectable 3-IPA. Mono-colonisation with Clostridium sporogenes alone restores production — the foundational organism-to-metabolite causal demonstration.

3-IPA treatment improved glucose tolerance and Akt phosphorylation in skeletal muscle in mice.

3-IPA inhibits gut dysbiosis and endotoxin leakage, attenuating steatohepatitis in rats.

Dietary 3-IPA supplementation reduces atherosclerotic plaque development in ApoE-knockout mice via reverse-cholesterol-transport promotion.

Clostridium sporogenes-derived metabolites (the mixture, not 3-IPA in isolation) protect mice against colonic inflammation.

Direct oral C. sporogenes supplementation (the organism, six weeks) increased body weight, fat mass, adipocyte size, serum triglycerides and hepatic lipogenesis gene expression in mice via enhanced intestinal energy/carbohydrate/fat absorption, despite unchanged feed intake. See the dedicated organism-vs-metabolite page for full treatment.

"Indolepropionic acid and novel lipid metabolites are associated with a lower risk of type 2 diabetes in the Finnish Diabetes Prevention Study" — a prospective cohort; higher serum 3-IPA associated with lower incident type 2 diabetes.

Decreased circulating 3-IPA identifies subjects with insulin resistance, overweight, low-grade inflammation and dysregulated branched-chain-amino-acid metabolism, in a multi-omics human study.

Circulating 3-IPA is lower in individuals with hepatic fibrosis than those without — a protective-direction association.

Integrated microbiome-metabolome analysis of coronary artery disease patients vs. controls (n=30+30), replicated in an independent atherosclerotic-cardiovascular-disease cohort (n=256) — lower 3-IPA associated with disease.

A randomized controlled-feeding trial in which the manipulated variable was diet (fried vs. non-fried meat), not 3-IPA. Fried-meat consumption lowered fecal 3-indolepropionic acid (and valeric/butyric acid); changes in these fecal cometabolites significantly associated with changes in insulin-sensitivity markers (IGI/MIRI).

A completed randomized trial of Cornelian cherry (Cornus mas) fruit lyophilizate vs. placebo in metabolic-syndrome patients (Wroclaw Medical University). Fecal indole-3-propionic acid is a named secondary outcome ("Change in Fecal Indole Metabolite Concentrations") alongside OGTT/insulin measures. Results not yet posted (hasResults=false).

OBSERVED_IN_SEARCH — CORRECTED 2026-09-10. Re-running this page's own documented query ("indole-3-propionic acid", ClinicalTrials.gov API v2) on 2026-09-10 returns 13 studies, including three registered trials that administer 3-IPA itself, all from the iPROACT programme at Glostrup University Hospital, Copenhagen (dietary-supplement indole-3-propionic acid vs. placebo; results not posted for any): NCT06674018 (iPROACT-pilot, completed 2025-02-25, 79 participants, healthy volunteers, first posted 2024-11-05), NCT07105514 (iPROACT-pilot2, recruiting, 32 participants estimated, first posted 2025-08-06) and NCT07318129 (iPROACT-MS, recruiting, 220 participants estimated, relapsing-remitting multiple sclerosis, completion estimated 2028-07-15, first posted 2026-01-05). None of the three tests a diabetes or glucose-regulation endpoint, so that specific gap is unchanged. All three were first posted before the 2026-09-05 search below, which recorded only 2 hits — the earlier return cannot be reconciled with the registry's first-posted dates, and both dated readings are kept on record.

3-IPA (or a C. sporogenes-based probiotic) could be developed as a preventive or adjunct approach for type 2 diabetes / metabolic syndrome. Extrapolated in review literature (Jiang H, et al., 2022, Nutrients, PMID 36615808; Roager & Licht, 2018, Nature Communications, PMID 30120222) from the mechanistic, cohort and animal evidence above.

3-IPA's antioxidant/free-radical-scavenging capacity meaningfully contributes to its metabolic-health associations in humans.

Clostridium sporogenes probiotic supplementation would be a beneficial, low-risk way to raise 3-IPA in humans.