Dietary Fiber, Gut Microbiota and Bile Acid Metabolism in Animals: Narrative Review on Animal Nutrition
This narrative review maps the dietary fiber–microbiota–bile acid axis in livestock species but provides no original experimental data or quantified effect sizes, precluding causal conclusions.
| Population | Non-ruminant production animals (swine, poultry) and ruminants of different species and physiological stages |
|---|---|
| Intervention | Dietary supplementation or variation of dietary fiber (soluble and insoluble: FOS, GOS, inulin, β-glucan, pectin, cellulose, lignin, among others) |
| Comparator | Control diets without supplemental fiber or with different types/levels of DF |
| Outcome | Gut microbiota composition; Secondary bile acid profile; Short-chain fatty acid (SCFA) production; Nutrient digestibility; Productive performance (weight gain, feed conversion); Intestinal immune function; Intestinal viscosity and gastrointestinal transit |
Summary of findings
| Outcome | Effect | 95% CI | Certainty | Clinical relevance | Notes |
|---|---|---|---|---|---|
| Gut microbiota composition | not quantified; narrative synthesis only | — | Very low | — | |
| Secondary bile acid profile | not quantified; narrative synthesis only | — | Very low | — | |
| Short-chain fatty acid (SCFA) production | not quantified; narrative synthesis only | — | Very low | — | |
| Nutrient digestibility | not quantified; narrative synthesis only | — | Very low | — | |
| Productive performance (weight gain, feed conversion) | not quantified; narrative synthesis only | — | Very low | — | |
| Intestinal immune function | not quantified; narrative synthesis only | — | Very low | — | |
| Intestinal viscosity and gastrointestinal transit | not quantified; narrative synthesis only | — | Very low | — |
Context
Dietary fiber (DF) modulates gut microbiota and bile acid (BA) metabolism in production animals, with implications for gut health, immunity, and productive performance. The relationship is bidirectional and species-dependent, complicating uniform recommendations. The absence of consolidated primary data justifies a narrative synthesis but limits the strength of conclusions.
What the study showed
The review describes that soluble DF is more fermentable and has a greater impact on microbial composition and secondary BA profiles than insoluble DF. In swine, excessive or inappropriate DF can increase intestinal viscosity, reduce digestibility, and impair performance. In poultry, soluble DF prolongs intestinal transit and creates a hypoxic environment that inhibits pathogens. No consolidated effect sizes (RR, OR, MD) are reported, as the text presents no meta-analysis or aggregated primary data.
How it was done
Narrative review (non-systematic) without pre-registered protocol, without explicitly described literature search, without formal inclusion/exclusion criteria, and without risk-of-bias assessment of included primary studies. Covers multiple species (swine, poultry, ruminants) and multiple DF types. Published in Veterinary Sciences (2026), DOI 10.3390/vetsci13020209.
Effect magnitude
No quantified effect size is provided. The review cites individual studies without statistically synthesizing their results, making it impossible to estimate an overall effect magnitude.
Risk of bias
Narrative design without PRISMA or equivalent protocol prevents formal risk-of-bias assessment (AMSTAR-2 and ROBINS-I tools not applied). Heterogeneity of species, DF types, doses, and outcomes precludes direct comparisons. Absence of original primary data and meta-analysis. Possible publication bias and reference selection bias by the author(s).
What this study does NOT prove
This review does not prove causality between any type of DF and any health or productive outcome in animals. It is not generalizable to species or physiological stages not represented in the cited primary studies.
In clinical practice
Clinicians and nutritionists should interpret recommendations from this review with caution: the described associations are biologically plausible but not supported by grade A or B evidence. Dietary DF adjustments in production animals must consider species, physiological stage, and specific fiber type, avoiding cross-species extrapolation. This study provides no basis for altering established diet formulation protocols.
Limitations
Narrative design without PRISMA or equivalent protocol prevents formal risk-of-bias assessment (AMSTAR-2 and ROBINS-I tools not applied). Heterogeneity of species, DF types, doses, and outcomes precludes direct comparisons. Absence of original primary data and meta-analysis. Possible publication bias and reference selection bias by the author(s).
What is still missing
Species- and production-stage-specific RCTs with defined doses of specific DF, simultaneously measuring microbiota, BA profile, and zootechnical performance with adequate sample sizes. Mechanistic studies quantifying the relative contribution of the DF→microbiota→BA pathway versus direct DF effects on BAs.
Technical appendix
Version history
- 1.0 · 2026-07-01 — Auto-generated under Evidence Standard v1.0