Dietary polyphenols and gut microbiota: narrative review on mechanistic interactions and human health
This narrative review describes interactions between dietary polyphenols and gut microbiota but generates no primary data and establishes no causal direction or quantifiable effect magnitude.
| Population | Humans (adults, general and disease populations including metabolic, neurological and inflammatory conditions); in vitro and in vivo (animal) models also included |
|---|---|
| Intervention | Dietary intake or supplementation of polyphenols (flavonoids, stilbenes, phenolic acids, lignans, tannins, among others) |
| Comparator | No formal comparator; narrative review without a defined control group |
| Outcome | Gut microbiota composition (Lactobacillus, Bifidobacterium, Akkermansia); Short-chain fatty acid (SCFA) production; Polyphenol bioavailability and metabolism; Metabolic disease outcomes (obesity, T2DM); Inflammatory bowel disease (IBD) outcomes; Neurological outcomes and gut-brain axis; Cardiovascular outcomes |
Summary of findings
| Outcome | Effect | 95% CI | Certainty | Clinical relevance | Notes |
|---|---|---|---|---|---|
| Gut microbiota composition (Lactobacillus, Bifidobacterium, Akkermansia) | No pooled estimate; narrative synthesis only; in the IC reported | — | Very low | — | |
| Short-chain fatty acid (SCFA) production | No pooled estimate; narrative synthesis only; in the IC reported | — | Very low | — | |
| Polyphenol bioavailability and metabolism | No pooled estimate; narrative synthesis only; in the IC reported | — | Very low | — | |
| Metabolic disease outcomes (obesity, T2DM) | No pooled estimate; narrative synthesis only; in the IC reported | — | Very low | — | |
| Inflammatory bowel disease (IBD) outcomes | No pooled estimate; narrative synthesis only; in the IC reported | — | Very low | — | |
| Neurological outcomes and gut-brain axis | No pooled estimate; narrative synthesis only; in the IC reported | — | Very low | — | |
| Cardiovascular outcomes | No pooled estimate; narrative synthesis only; in the IC reported | — | Very low | — |
Context
Gut microbiota modulates metabolism, immunity and epithelial barrier function. Polyphenols are metabolised by gut bacteria into bioactive metabolites with potential systemic effects. The bidirectional relationship between polyphenols and microbiota is biologically plausible but causal evidence in humans remains limited.
What the study showed
The study narratively synthesises that polyphenols favour growth of Lactobacillus, Bifidobacterium and Akkermansia muciniphila and reduce potentially pathogenic bacteria. No primary data are generated; no pooled effect size, 95% CI or p-value is calculated by the review itself. Findings derive from heterogeneous primary studies, including animal and in vitro models, without quantitative synthesis.
How it was done
Narrative review searching PubMed, Web of Science, Embase, ScienceDirect and Scopus; period 2011–2025; three independent reviewers assessed eligibility by title and abstract. Exclusion criteria deliberately eliminated systematic reviews and meta-analyses. No PROSPERO protocol was registered, no standardised data extraction was performed and no formal risk-of-bias assessment of included studies was conducted.
Effect magnitude
No pooled effect size is reported by this review. Individual data from cited primary studies are not synthesised with 95% CI or formal statistics.
Risk of bias
Narrative review without registered protocol, without risk-of-bias assessment (RoB 2, ROBINS-I or AMSTAR-2 tools were not applied) and without quantitative synthesis. Heterogeneity of models (in vitro, animal, human) precludes direct extrapolation. Publication bias was not assessed. Deliberate exclusion of meta-analyses and systematic reviews reduces the evidence level of the synthesis.
What this study does NOT prove
This review does not prove causality between polyphenol consumption and improved clinical outcomes in humans. Findings from animal and in vitro models cannot be generalised to specific clinical populations.
In clinical practice
This review does not provide sufficient basis to modify clinical practice. Clinicians may consider polyphenol-rich diets as a component of general healthy eating, but no dose, duration or validated target species from robust clinical trials supports specific supplementation. Await RCTs with well-defined primary clinical outcomes before recommending targeted polyphenol supplementation.
Limitations
Narrative review without registered protocol, without risk-of-bias assessment (RoB 2, ROBINS-I or AMSTAR-2 tools were not applied) and without quantitative synthesis. Heterogeneity of models (in vitro, animal, human) precludes direct extrapolation. Publication bias was not assessed. Deliberate exclusion of meta-analyses and systematic reviews reduces the evidence level of the synthesis.
What is still missing
RCTs with defined populations, standardised doses of specific polyphenols, primary clinical outcomes and long-term microbiota monitoring by sequencing are needed to establish causality and effect magnitude.
Technical appendix
Version history
- 1.0 · 2026-11-06 — Auto-generated under Evidence Standard v1.0