Re-evaluating gut microbiome signatures of post-antibiotic dietary fiber intake in a large adult cohort
High-fiber intake post-antibiotic did not increase alpha diversity and did not uniformly enrich commensal Clostridia; it favored Bifidobacterium and Lachnospira over the low-fiber group.
| Population | Adults with recent antibiotic exposure (within one month), participants in the American Gut Project (AGP) |
|---|---|
| Exposure | High dietary fiber intake (HF, N = 971) |
| Comparator | Low dietary fiber intake (LF, N = 955) |
| Outcome | Post-antibiotic alpha diversity; Bifidobacterium abundance (high fiber vs. low fiber group); Lachnospira abundance (high fiber vs. low fiber group); Bacteroides abundance (low fiber vs. high fiber group); Microbiome composition (beta diversity); Commensal Clostridia enrichment |
Summary of findings
| Outcome | Effect | 95% CI | Certainty | Clinical relevance | Notes |
|---|---|---|---|---|---|
| Post-antibiotic alpha diversity | no significant difference, effect size not reported | — | Low | — | 1 studies |
| Bifidobacterium abundance (high fiber vs. low fiber group) | P < 0.001, effect size and 95% CI not reported | — | Low | — | 1 studies |
| Lachnospira abundance (high fiber vs. low fiber group) | P < 0.001, effect size and 95% CI not reported | — | Low | — | 1 studies |
| Bacteroides abundance (low fiber vs. high fiber group) | enriched in LF group, P < 0.001, effect size and 95% CI not reported | — | Low | — | 1 studies |
| Microbiome composition (beta diversity) | difference reported, statistics not fully reported in available text | — | Low | — | 1 studies |
| Commensal Clostridia enrichment | no uniform enrichment in HF group; effect size not reported | — | Low | — | 1 studies |
Context
Antibiotic use is a primary driver of gut dysbiosis, and rapid microbiome recovery is clinically relevant to prevent opportunistic infections such as Clostridioides difficile. Prior studies suggested high-fiber diets promoted recovery via commensal Clostridia, but were based on small cohorts (n ≤ 30). This study tests that hypothesis in a substantially larger sample using observational data from the American Gut Project.
What the study showed
High fiber intake was not associated with uniform enrichment of commensal Clostridia, contradicting prior models. Bifidobacterium and Lachnospira were identified as genus-level biomarkers enriched in the HF group; Bacteroides and Parabacteroides were more abundant in the LF group. These associations were confirmed by multivariable linear regression (P < 0.001). Alpha diversity was not significantly higher in the HF group within the one-month post-antibiotic window. Absolute abundance values, 95% CIs, and effect sizes were not reported in the available text.
How it was done
Cross-sectional observational study using publicly available 16S rRNA gene (V4 region) sequencing data from the American Gut Project. Participants stratified by high (N = 971) or low (N = 955) fiber intake among those with recent antibiotic exposure. Alpha and beta diversity analysis, LEfSe for differential abundance, validation by ANCOM-BC, and multivariable linear regression adjusted for age, sex, and BMI.
Effect magnitude
The study reports statistical significance (P < 0.001) for genus-level biomarkers but provides no quantitative effect sizes (SMD, MD, OR, RR) or 95% CIs for primary outcomes in the available text. Clinical magnitude remains undetermined.
Risk of bias
Cross-sectional observational design precludes causal inference; residual confounding by antibiotic type, treatment duration, and other dietary variables cannot be excluded. Fiber intake was self-reported (food frequency), subject to recall and misclassification bias. No formal risk-of-bias assessment tool (ROBINS-I) was applied. The one-month post-antibiotic window is self-reported and imprecise.
What this study does NOT prove
This study does not prove that high fiber intake causes post-antibiotic microbiome recovery or that the observed taxonomic differences produce measurable clinical benefits. Data are cross-sectional and associative, without control for antibiotic type or duration.
In clinical practice
Clinicians should not assume high-fiber diets broadly restore the microbiome or increase diversity in the short-term post-antibiotic period. Bifidobacterium and Lachnospira represent genus-specific targets associated with high fiber intake, but the functional clinical relevance of these taxonomic differences is not established. Post-antibiotic nutritional recommendations should be interpreted with caution.
Limitations
Cross-sectional observational design precludes causal inference; residual confounding by antibiotic type, treatment duration, and other dietary variables cannot be excluded. Fiber intake was self-reported (food frequency), subject to recall and misclassification bias. No formal risk-of-bias assessment tool (ROBINS-I) was applied. The one-month post-antibiotic window is self-reported and imprecise.
What is still missing
Randomized controlled trials with controlled dietary intervention and longitudinal microbiome monitoring are needed to establish causality and define the magnitude of functional benefit of high-fiber diets in the post-antibiotic period.
Technical appendix
Version history
- 1.0 · 2026-07-11 — Auto-generated under Evidence Standard v1.0