# Video research-update insert: Gut microbial community composition as a primary systemic cause

Editorial script and storyboard insert, 5 October 2026. No rendered video. Read alongside the original review; no new grade is announced.

## Narration

Microbiota can causally influence systemic phenotypes in defined models and selected human settings. Engraftment, clinical benefit and disease initiation remain different claims; positive and null FMT studies prevent a universal intervention narrative.

In the 2010 study, a defined commensal species restored Th17-related autoimmunity and arthritis in susceptible mice. Host genotype and immune context are part of the demonstrated causal system. [P20620945]

In the 2020 study, engraftment occurred without clinically significant metabolic effects during follow-up. Microbial target engagement is insufficient to assume systemic efficacy. [P32150549]

In the 2025 study, microbial/metabolite differences appeared without reproducing metabolic or behavioural obesity phenotypes. A bounded transfer null does not erase effects under other diets or host conditions. [P40316655]

The next discriminating question is: Which host, donor and dietary context determines efficacy? Microbial functions may require permissive host ecology or dietary substrate. Factorial donor/function-by-diet testing with colonization measures; prespecified host phenotypes and independent recipient replication.

The timeline shows selected changes in evidence, not inevitable progress or proof of a single cause. The review’s archived grade remains unchanged; the depth of source reading is documented in the update.

## Storyboard and source locks

| Insert | Visual | Narration anchor | Sources |
|---|---|---|---|
| Opening | Claim and bounded update statement | First paragraph | Review claim and source ledger |
| Timeline 2010 | Dated study card with design, result and limit | A defined commensal species restored Th17-related autoimmunity and arthritis in susceptible mice. | [P20620945](https://pubmed.ncbi.nlm.nih.gov/20620945/) |
| Timeline 2020 | Dated study card with design, result and limit | Engraftment occurred without clinically significant metabolic effects during follow-up. | [P32150549](https://pubmed.ncbi.nlm.nih.gov/32150549/) |
| Timeline 2025 | Dated study card with design, result and limit | Microbial/metabolite differences appeared without reproducing metabolic or behavioural obesity phenotypes. | [P40316655](https://pubmed.ncbi.nlm.nih.gov/40316655/) |
| G1 | Question → competing explanation → discriminating test | Which host, donor and dietary context determines efficacy? | [P24009397](https://pubmed.ncbi.nlm.nih.gov/24009397/), [P28978426](https://pubmed.ncbi.nlm.nih.gov/28978426/), [P32150549](https://pubmed.ncbi.nlm.nih.gov/32150549/), [P40316655](https://pubmed.ncbi.nlm.nih.gov/40316655/) |
| G2 | Question → competing explanation → discriminating test | Does engraftment deliver a durable systemic effect? | [P22728514](https://pubmed.ncbi.nlm.nih.gov/22728514/), [P28978426](https://pubmed.ncbi.nlm.nih.gov/28978426/), [P32150549](https://pubmed.ncbi.nlm.nih.gov/32150549/) |
| G3 | Question → competing explanation → discriminating test | What explains opposing Parkinson trial results? | [P38686220](https://pubmed.ncbi.nlm.nih.gov/38686220/), [P39073834](https://pubmed.ncbi.nlm.nih.gov/39073834/) |
| G4 | Question → competing explanation → discriminating test | Does a microbial change initiate disease or modify an established disease? | [P20620945](https://pubmed.ncbi.nlm.nih.gov/20620945/), [P26633628](https://pubmed.ncbi.nlm.nih.gov/26633628/), [P39800192](https://pubmed.ncbi.nlm.nih.gov/39800192/), [P32150549](https://pubmed.ncbi.nlm.nih.gov/32150549/) |

## Editorial constraints

- Use the primary-source links shown above and keep the inference limit on screen with each milestone.
- Do not narrate an abstract check as complete-paper examination, a model result as human proof, or an unresolved inference as absence of all research.
- Preserve trial endpoint hierarchy, cohort reuse, correction notices and online/issue dates.
- Use original graphics made from this ledger. Publisher figure imagery has not been cleared or supplied for video reuse.
- Confirm any change in verdict through a separate documented HSEF review; this insert makes none.