Fecal microbiota transplant (FMT)

Transfer of processed fecal material from a healthy donor to a recipient’s gastrointestinal tract with the goal of restoring or modifying the recipient’s gut microbial community. The only intervention with direct evidence that the gut microbiome causally influences host lifespan in a vertebrate model (killifish; Smith 2017 ¹). In rCDI it is FDA-approved and standard-of-care; in aging it is investigational only, with active Phase 1/2 trials but no hard-endpoint RCT completed.

Mode classification rationale

FMT is classified as mode: dietary rather than mode: stem-cell-therapy for two reasons: (1) the wiki has no microbiome-therapy mode class, and (2) FMT delivers a microbial community via the gut — an oral or enteral route biologically analogous to dietary supplementation. It is not autologous cell therapy, does not involve surgical engraftment of tissue, and its mechanism of action is primarily metabolic (SCFA restoration, bile-acid metabolism, pathobiont displacement) rather than cell-type repopulation. If a dedicated mode: microbiome-therapy value is ever added to the CLAUDE.md schema, this page should be updated. unsourced — this mode decision is a wiki-schema choice, not a medical classification.

Established medical use — rCDI (indication anchor)

FMT for recurrent Clostridioides difficile infection (rCDI) is the only FDA-approved microbiome-intervention indication:

Product	Approval	Route	Sponsor	Notes
Rebyota (RBX2660)	Nov 2022	Rectal enema	Ferring Pharmaceuticals	Live suspension; >8 wk post-antibiotic CDI course
Vowst (SER-109)	Apr 2023	Oral capsule (4 caps × 3 days)	Seres Therapeutics	Lyophilized spore-enriched oral product; first orally administered microbiome therapeutic

These products establish FMT as clinically validated and safe at the population level for the rCDI indication — but this evidence does not transfer to the aging indication. The immunological context, donor-selection criteria, dosing, and outcome measures are entirely different.

Delivery routes

Nasoduodenal / nasogastric tube — most common in early clinical studies; avoids upper GI acid environment
Colonoscopic instillation — deeper delivery to colon; historically the most common route; allows mucosal inspection
Retention enema — lower-cost; patient-administered; suitable for rectal-reaching pathobionts
Oral capsules (lyophilized) — Vowst/SER-109 is the proof of concept; requires spore-forming survival through gastric acid; patient-friendly
Washed microbiota transplant (WMT) — centrifugation-enriched preparation that removes inflammatory proteins in donor stool; lower adverse-event profile than crude FMT (theoretical)
Sterile fecal filtrate transfer (FFT) — bacteriophage-enriched filtrate with no live bacteria; tests whether soluble components and phage mediate CDI protection independent of bacterial engraftment

Mechanisms of action (aging context)

FMT’s aging-relevant effects are hypothesised through several interconnected mechanisms:

Mechanism	Detail	Evidence status
SCFA restoration	Young/healthy donors supply butyrate-producing Roseburia, Faecalibacterium prausnitzii — displacing age-associated Enterobacteriaceae; butyrate feeds colonocytes, suppresses NF-κB, and induces autophagy	Mechanistic; see scfa-signaling
Pathobiont displacement	Gram-negative Proteobacteria (LPS producers) decline as butyrate-producers engraft; lower systemic LPS → reduced TLR4-mediated inflammaging	Demonstrated in progeroid-mouse FMT study ²
Bile acid normalization	Secondary bile acids (deoxycholic acid, lithocholic acid) require intact gut flora for 7α-dehydroxylation; dysbiosis impairs this; FMT restores secondary BA profile, modulating FXR/TGR5 signalling	Bárcena 2019 identified secondary BA shifts ²
Immune modulation	Gut microbiome controls regulatory T-cell induction and gut-barrier tight-junction integrity; “young” community resets the gut-associated lymphoid tissue environment	Boehme 2021: young-FMT recipients showed reversed immune alterations in peripheral tissues and brain ³
Akkermansia	A. muciniphila is the hallmark mucus-layer maintainer; depleted in aged guts; Bárcena 2019 showed transplantation of A. muciniphila alone recapitulated key benefits of full FMT in progeroid mice	See akkermansia-muciniphila

Animal model evidence

Killifish (N. furzeri) — heterochronic FMT

Smith et al. 2017 colonised middle-aged killifish (9.5 weeks of age, near their median lifespan in captivity of 4–8 months) with gut bacteria from young fish (6 weeks) following antibiotic depletion of resident microbiota. Young-microbiota recipients (Ymt) showed 37% median lifespan extension vs untreated wild-type controls (Logrank p = 4.04E-09), 41% vs same-age microbiota recipients (Omt; p = 5.08E-06), and delayed behavioural decline (preserved spontaneous locomotor activity at 16 weeks) ¹. This is the first direct vertebrate demonstration that the gut microbiome causally influences lifespan. Killifish are the most tractable vertebrate model for lifespan studies given their ~3–6 month lifespan in captivity. needs-human-replication — killifish are phylogenetically distant from humans; the translational relevance of fish gut microbiome manipulation to human aging is unknown.

Dimension	Status
Pathway conserved in humans?	partial — SCFA/microbiome-immune axis conserved; killifish microbiome composition very different
Phenotype conserved in humans?	unknown
Replicated in humans?	no

Progeroid mice (Lmna^G609G^) — young→progeroid FMT

Bárcena et al. 2019 administered FMT from healthy wild-type donors to progeria-model (Lmna^G609G/G609G^) mice and found extended healthspan and lifespan (13.5% increase in median lifespan, 160 vs 141 days, P = 0.0029), along with intestinal dysbiosis reversal (elevated Proteobacteria and Cyanobacteria in progeria reduced; Verrucomicrobia/Akkermansia restored) ². Transplantation of A. muciniphila alone was sufficient to exert beneficial effects. Secondary bile acid profiles were also normalised.

Dimension	Status
Pathway conserved in humans?	partial — Lmna progeria model is mechanistically distinct from normal aging; Proteobacteria-dysbiosis pattern is shared
Phenotype conserved in humans?	unknown — no equivalent human trial
Replicated in humans?	no

Centenarian → young mice FMT

Chen et al. 2020 transferred fecal microbiota from a single 101-year-old long-living donor (L group) into 11-month-old C57BL/6 mice (n=16 total; ~8 per group), using an elderly 70-year-old donor as the control group (E group). L-group recipients showed increased alpha-diversity, expansion of probiotic genera (Lactobacillus, Bifidobacterium) and SCFA-producing genera (Roseburia, Faecalibacterium, Ruminococcus, Coprococcus), reduced lipofuscin (brain, p<0.05) and senescence-associated β-galactosidase accumulation (heart and ileum, p<0.0001), and elongated intestinal villi (p<0.001) compared to E-group controls ⁴. needs-replication — single study; one centenarian donor only; mice were middle-aged not young at baseline; translational relevance to human aging unclear.

Young → aged mice — cognitive reversal

Boehme et al. 2021 transplanted microbiota from 3–4-month-old mice into 19–20-month-old recipients. Young-microbiota transplants reversed aging-related immune alterations in peripheral tissues and brain, modified hippocampal metabolome and transcriptome, and attenuated selective cognitive impairments in aged hosts ³. This is the primary preclinical anchor for FMT-aging-cognition trials. needs-human-replication. Note: specific n per group, p-values, and effect sizes are unverified (paper is closed-access) no-fulltext-access.

Human evidence — aging indication

No published large-sample RCT exists for FMT in normal aging or frailty as of May 2026. Evidence is limited to:

Case reports / case series — several case reports describe cognitive improvement after FMT in Alzheimer’s patients; no controlled studies have been published. These are hypothesis-generating only.
Observational data from rCDI cohorts — rCDI disproportionately affects older adults; some rCDI cohorts have reported secondary frailty or cognitive trajectories post-FMT, but these are not powered or designed to test aging outcomes.
Phase 1/2 trials (active as of 2026-05-07): three trials retrieved from ClinicalTrials.gov v2 API:
- NCT05598112 — “Effect of FMT on Aging and the Underlying Mechanisms” (Early Phase 1)
- NCT06649981 — “Aging Resilience Through Microbiota Optimization and Regulation” (Phase 1)
- NCT06496412 — “Safety and Efficacy of FMT on Cognitive Function” (no phase; n=40-210 range)

These trials are ongoing; no results have been published from aging-specific endpoints. clinical-trials-active: 3 as of 2026-05-07.

Donor selection and the super-donor hypothesis

Donor screening for clinical FMT is extensive: stool cultures (enteric pathogens, C. difficile toxin), blood serology (HIV, HCV, HBV, CMV, EBV, HTLV), antibiotic-resistance gene screening (ESBL, carbapenemase, MRSA, VRE), parasite panels, and exclusion criteria for recent antibiotic use, IBD, autoimmune disease, and obesity.

The super-donor hypothesis proposes that a minority of donors produce fecal material with disproportionately high engraftment rates and clinical response — possibly due to phage composition, SCFA-producer abundance, or immunomodulatory strains. If valid, donor stratification rather than universal FMT could dramatically improve efficacy. Currently supported by observational data from IBS and IBD FMT trials but not yet validated in aging trials. no-mechanism — the biological basis of super-donor efficacy is unresolved.

For aging applications, the additional dimension of donor age is critical: should the donor be young (to supply a “young-like” microbiome for heterochronic benefit), or healthy-aged (for immunological compatibility)? No aging RCT has resolved this.

Comparison with other dysbiosis interventions

Intervention	Mechanism	Evidence tier (aging)	Hallmark coverage	Link
FMT	Community restoration; engraftment of donor strains	Preclinical strong; human limited	dysbiosis, chronic-inflammation	this page
Prebiotics	Substrate supply (fibre); enriches SCFA-producing species indirectly	Human observational	dysbiosis	prebiotics
Probiotics	Single- or multi-strain supplementation	Human limited; small RCTs	dysbiosis	lactobacillus, bifidobacterium
Postbiotics	Microbial metabolites or heat-inactivated bacteria; no live cells	Preclinical/limited human	dysbiosis	postbiotics
Akkermansia supplementation	Specific mucus-layer restorer; postbiotic or live	Phase 2 (MetaboAge)	dysbiosis, gut-barrier	akkermansia-muciniphila

FMT is the only intervention that delivers the complete community — donor phage, SCFA producers, secondary-bile-acid converters, and immune-modulatory strains simultaneously. This is both its mechanistic advantage and its regulatory complexity.

Safety profile

rCDI indication — well-established

In rCDI populations (typically elderly or immunocompromised patients receiving antibiotics), Rebyota and Vowst have well-established safety profiles from Phase 3 RCTs. The most common adverse events are gastrointestinal (bloating, cramping, flatulence) and self-limiting.

Aging/healthy-population indication — investigational

Critical safety caveat: In 2019, a high-profile NEJM case series (DeFilipp et al.) documented two immunocompromised patients who developed ESBL-producing E. coli bacteremia after receiving FMT from a shared donor; one died ⁵. The source was an inadequately screened donor with ESBL carriage. This prompted the FDA to issue a safety alert and require ESBL screening in donor stool.

Relevance for aging: older adults have higher rates of immune senescence and are partially overlapping with the “immunocompromised” population at risk. A 2023 donor-screening study found 35.2% (56/159) of donor stools carried ESBL-producing organisms and 31.4% carried diarrheagenic E. coli — even after initial health screening ⁶. Rigorous multi-step screening is essential.

Additional long-term unknowns:

Engraftment durability: how long donor strains persist; whether re-administration is needed
Downstream host-microbiome co-evolution: whether donor strains alter host immune set-points in unpredictable ways at long timeframes
Cancer risk: theoretical concern that specific microbiome profiles (e.g., Fusobacterium nucleatum enrichment) could increase colorectal cancer risk — no evidence in FMT recipients but not excluded

Limitations and gaps

needs-human-replication — all lifespan/healthspan evidence is in fish or mice; no human aging RCT has completed
long-term-unknown — durability of microbiome engraftment after single FMT in aging context is unstudied; rCDI recipients show engraftment waning over months
dose-response-unclear — optimal donor age, preparation method, route, and dosing frequency for aging indication are entirely undefined
needs-replication — Chen 2020 (centenarian → middle-aged mouse) is a single study with one centenarian donor; no independent replication
no-mechanism — super-donor biology and predictors of FMT engraftment success are unresolved
The progeroid-mouse model (Bárcena 2019) is an accelerated-aging model mechanistically distinct from normal chronological aging; translation confidence is low

Cross-references

dysbiosis — primary hallmark targeted
gut-microbiome-aging-shifts — detailed taxonomy of age-associated compositional shifts
gut-barrier — FMT effects on tight-junction integrity and mucus layer
chronic-inflammation — downstream consequence of dysbiosis; FMT target via LPS/SCFA axis
scfa-signaling — key effector pathway
akkermansia-muciniphila — key commensal restored by FMT; single-species transplant recapitulates partial FMT benefit in Bárcena 2019
bifidobacterium — age-depleted probiotic genus enriched by FMT from centenarian donors
lactobacillus — probiotic genus transferred in centenarian-donor FMT; expanded in Chen 2020 recipients
prebiotics — substrate-only alternative; weaker community-restructuring effect
postbiotics — metabolite-bypass alternative; no live microbes; different regulatory category
altered-intercellular-communication — gut-systemic axis; microbiome signals are intercellular communication between host and microbial cells

Footnotes

doi:10.7554/eLife.27014 · in-vivo (killifish, Nothobranchius furzeri) · randomised microbiota transplant from young (6-wk) to middle-aged (9.5-wk) recipients after antibiotic depletion; controls: antibiotic-only (Abx), same-age microbiota (Omt), untreated wild-type (wt) · 37% median lifespan extension vs wt (Logrank p = 4.04E-09); 41% vs Omt (p = 5.08E-06); 21% vs Abx (p = 5.89E-05); delayed locomotor decline · local PDF available · citation percentile: 100 (n=402 citations, FWCI 20.2) ↩ ↩²
doi:10.1038/s41591-019-0504-5 · in-vivo (progeroid Lmna^G609G/G609G^ mice; two models also validated in Zmpste24^-/-^) · FMT from healthy WT donors → progeria mice · 13.5% median lifespan extension (160 vs 141 days, P=0.0029); 9% maximal survival increase (P=0.04); dysbiosis reversal (Proteobacteria/Cyanobacteria reduced, Verrucomicrobia restored); A. muciniphila oral gavage alone achieved modest lifespan extension (P=0.016); secondary bile acid profile normalised · citation percentile: 100 (n=613 citations, FWCI 29.5) ↩ ↩² ↩³
doi:10.1038/s43587-021-00093-9 · in-vivo (aged C57BL/6 mice 19–20 mo) · young-microbiota FMT from 3–4 mo donors · reversed aging-related immune alterations in peripheral tissues and brain; attenuated selective cognitive impairments; hippocampal metabolome + transcriptome modified · not_oa; PDF not in archive — quantitative claims (n per group, specific p-values, effect sizes) unverified against full text no-fulltext-access · citation percentile: 100 (n=284 citations, FWCI 24.7) ↩ ↩²
doi:10.18632/aging.102872 · in-vivo (11-month-old C57BL/6 mice; n=16 total, ~8/group) · FMT from one 101-year-old long-living donor (L group) vs one 70-year-old elderly donor (E group) · increased α-diversity; expanded Lactobacillus/Bifidobacterium and SCFA-producing genera; reduced lipofuscin (brain p<0.05) and SA-β-gal (heart/ileum p<0.0001); elongated intestinal villi (p<0.001) · OA via PMC7138539 ↩
doi:10.1056/NEJMoa1910437 · case-series (NEJM Brief Report) · 2 immunocompromised FMT recipients (Patient 1: hepatic encephalopathy trial NCT03420482; Patient 2: HCT trial NCT03720392) · ESBL-producing E. coli bacteremia transmitted from shared inadequately-screened donor (2018 FDA protocol did not require ESBL screening); 1 death (Patient 2) · prompted FDA 2019 safety alert requiring ESBL donor-stool screening · local PDF available · citation percentile: 100 (n=1092 citations, FWCI 97.6) ↩
doi:10.1007/s10096-023-04644-3 · observational (donor-screening audit) · n=159 stool samples · 35.2% ESBL carriage; 31.4% diarrheagenic E. coli carriage; only 5% (37/742) initial candidates qualified post-screening · model: clinical FMT donor bank · not_oa; PDF not in archive — percentages unverified against full text no-fulltext-access ↩

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