Interactions between Dietary Antioxidants, Dietary Fiber and the Gut Microbiome: Their Putative Role in Inflammation and Cancer
This non-experimental narrative review maps proposed mechanisms linking diet, gut microbiome, and disease without generating its own effect estimates or establishing causality.
| Population | General human population (no specific age group, clinical condition, or demographic characteristic defined) |
|---|---|
| Intervention | Dietary antioxidants and dietary fiber as modulators of the gut microbiome |
| Comparator | — |
| Outcome | Gut microbiome composition modulation by dietary antioxidants; Gut microbiome composition modulation by dietary fiber; Systemic inflammatory markers; Colorectal cancer risk or incidence; Microbial metabolite production (SCFAs) |
Summary of findings
| Outcome | Effect | 95% CI | Certainty | Clinical relevance | Notes |
|---|---|---|---|---|---|
| Gut microbiome composition modulation by dietary antioxidants | not calculable — narrative review, in the pooled estimate | — | Very low | — | |
| Gut microbiome composition modulation by dietary fiber | not calculable — narrative review, in the pooled estimate | — | Very low | — | |
| Systemic inflammatory markers | not calculable — narrative review, in the pooled estimate | — | Very low | — | |
| Colorectal cancer risk or incidence | not calculable — narrative review, in the pooled estimate | — | Very low | — | |
| Microbial metabolite production (SCFAs) | not calculable — narrative review, in the pooled estimate | — | Very low | — |
Context
The relationship between diet, gut microbiota, and chronic diseases such as cancer is a growing area of investigation. Narrative reviews synthesize the state of the field but do not replace systematic reviews with meta-analysis. The absence of a registered protocol and formal risk-of-bias assessment limits the inferential weight of this publication.
What the study showed
The study collected no primary data and conducted no meta-analysis: it narratively compiled prior studies. The authors propose that dietary antioxidants (vitamins, flavonoids, carotenoids) and dietary fiber modulate microbiota composition and, consequently, inflammatory and carcinogenic pathways. No effect size, 95% CI, or heterogeneity test was calculated by the authors themselves. The associations described derive from primary studies of heterogeneous design and quality, including animal models and observational studies.
How it was done
Narrative (non-systematic) review of literature published between 2005 and 2024, retrieved from multiple databases with predefined keywords. No protocol registration, PRISMA criteria, risk-of-bias assessment (AMSTAR-2 not applicable due to absence of meta-analysis), or reproducible search strategy with adequate detail is reported. The total number of included studies is not stated.
Effect magnitude
No effect size was calculated by this review. Numerical data cited belong to individual primary studies, not consolidated here.
Risk of bias
Narrative review with no registered protocol, no formal risk-of-bias assessment (AMSTAR-2 inapplicable; appropriate tools would be SANRA or Baxter scale for narrative reviews), and no quantitative synthesis. Study selection is potentially subject to confirmation bias. Heterogeneity of primary designs (in vitro, animal, observational, RCT) precludes unified causal conclusions.
What this study does NOT prove
This study does not prove that dietary antioxidants or fiber prevent or treat cancer, nor that they modulate the microbiome in a clinically relevant manner in humans. It does not establish causality, dose-response, or generalizability to populations with specific clinical conditions.
In clinical practice
This review does not provide sufficient basis to change clinical practice in isolation. Clinicians may use the document as a conceptual map to identify research gaps, but therapeutic decisions require evidence from robust RCTs or meta-analyses. Recommendations to increase dietary fiber and antioxidants already exist in evidence-based guidelines independent of this review.
Limitations
Narrative review with no registered protocol, no formal risk-of-bias assessment (AMSTAR-2 inapplicable; appropriate tools would be SANRA or Baxter scale for narrative reviews), and no quantitative synthesis. Study selection is potentially subject to confirmation bias. Heterogeneity of primary designs (in vitro, animal, observational, RCT) precludes unified causal conclusions.
What is still missing
Long-duration RCTs evaluating hard clinical outcomes (cancer incidence, mortality, measurable inflammatory events) with standardized dietary interventions and metagenomic characterization of the microbiome are needed to establish causality.
Technical appendix
Version history
- 1.0 · 2026-06-21 — Auto-generated under Evidence Standard v1.0