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Meta-Analysis
. 2025 Feb 1;83(2):e4-e24.
doi: 10.1093/nutrit/nuae002.

The effect of oral synbiotics on the gut microbiota and inflammatory biomarkers in healthy adults: a systematic review and meta-analysis

Denelle J Cosier  1 , Kelly Lambert  1 , Elizabeth P Neale  1 , Yasmine Probst  1 , Karen Charlton  1
Affiliations
Meta-Analysis

The effect of oral synbiotics on the gut microbiota and inflammatory biomarkers in healthy adults: a systematic review and meta-analysis

Denelle J Cosier et al. Nutr Rev. .

Abstract

Context: Prior research has explored the effect of synbiotics, the combination of probiotics and prebiotics, on the gut microbiota in clinical populations. However, evidence related to the effect of synbiotics on the gut microbiota in healthy adults has not been reviewed to date.

Objective: A systematic review and meta-analysis was conducted to comprehensively investigate the effect of synbiotics on the gut microbiota and inflammatory markers in populations of healthy adults.

Data sources: Scopus, PubMed, Web of Science, ScienceDirect, MEDLINE, CINAHL, and The Cochrane Library were systematically searched to retrieve randomized controlled trials examining the primary outcome of gut microbiota or intestinal permeability changes after synbiotic consumption in healthy adults. Secondary outcomes of interest were short-chain fatty acids, inflammatory biomarkers, and gut microbiota diversity.

Data extraction: Weighted (WMD) or standardized mean difference (SMD) outcome data were pooled in restricted maximum likelihood models using random effects. Twenty-seven articles reporting on 26 studies met the eligibility criteria (n = 1319).

Data analysis: Meta-analyses of 16 studies showed synbiotics resulted in a significant increase in Lactobacillus cell count (SMD, 0.74; 95% confidence interval [CI], 0.15, 1.33; P = 0.01) and propionate concentration (SMD, 0.22; 95% CI, 0.02, 0.43; P = 0.03) compared with controls. A trend for an increase in Bifidobacterium relative abundance (WMD, 0.97; 95% CI, 0.42, 2.52; P = 0.10) and cell count (SMD, 0.82; 95% CI, 0.13, 1.88; P = 0.06) was seen. No significant differences in α-diversity, acetate, butyrate, zonulin, IL-6, CRP, or endotoxins were observed.

Conclusion: This review demonstrates that synbiotics modulate the gut microbiota by increasing Lactobacillus and propionate across various healthy adult populations, and may result in increased Bifidobacterium. Significant variations in synbiotic type, dose, and duration should be considered as limitations when applying findings to clinical practice.

Systematic review registration: PROSPERO no. CRD42021284033.

Keywords: gut microbiome; gut microbiota; healthy adult; inflammation; prebiotic; probiotic; symbiotic.

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Figures

Figure 1
Figure 1
Flow diagram of the literature search process. Abbreviation: PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses.
Figure 2
Figure 2
Forest plot of weighted standardized mean differences or standardized mean difference and 95% CIs for synbiotics compared with control. (A) Lactobacillus cell count; (B) Bifidobacterium cell count; and (C) Bifidobacterium relative abundance. Abbreviations: CI, confidence interval; REML, restricted maximum likelihood.
Figure 3
Figure 3
Forest plot of weighted mean difference or standardized mean difference and 95% CIs for synbiotics compared with control. (A) Zonulin; (B) Shannon Index; (C) acetate concentration: (D) propionate concentration; and (E) butyrate concentration. Abbreviations: CI, confidence interval; REML, restricted maximum likelihood.
Figure 4
Figure 4
Forest plot of weighted mean difference and 95% CIs for synbiotics compared with control. (A) Interleukin-6; (B) CRP; and (C) endotoxin. Abbreviations: CI, confidence interval; CRP, C-reactive protein; REML, restricted maximum likelihood.
Figure 5
Figure 5
Risk of bias as a weighted proportion of total studies.
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