Synbiotic supplementation and gut microbiota composition in children and adolescents with exogenous obesity (Probesity-2 trial)
Twelve weeks of multispecies synbiotic reduced the Firmicutes/Bacteroidetes ratio and altered microbiota composition in obese children, but alpha diversity decreased in the intervention group and the study does not establish clinical benefit independent of concurrent diet and physical activity.
| Population | Children and adolescents with exogenous obesity |
|---|---|
| Intervention | Oral synbiotic (L. acidophilus, L. rhamnosus, B. bifidum, B. longum, E. faecium — 2.5×10⁹ CFU/sachet + FOS 625 mg/sachet) for 12 weeks, combined with standard diet and increased physical activity |
| Comparator | Oral placebo for 12 weeks, with same diet and physical activity |
| Outcome | Firmicutes/Bacteroidetes ratio; Alpha diversity (observed OTUs and Chao1); Relative abundance of Bacteroidetes; Relative abundance of Prevotella; Relative abundance of Dialister; Beta-diversity composition (phylum level); Dominance of specific species (Collinsella stercoris vs. Bacteroides eggerthi) |
Summary of findings
| Outcome | Effect | 95% CI | Certainty | Clinical relevance | Notes |
|---|---|---|---|---|---|
| Firmicutes/Bacteroidetes ratio | synbiotic: 3.54 to 2.75 (p<0.05); placebo: 4.70 to 3.54 (p<0.05); between-group difference at endpoint p<0.05; 95% CI not reported | — | Low | — | 1 studies |
| Alpha diversity (observed OTUs and Chao1) | decrease in synbiotic group vs baseline (p<0.001 for both OTUs and Chao1); in the change in placebo group; 95% CI not reported | — | Low | — | 1 studies |
| Relative abundance of Bacteroidetes | synbiotic group: 18.8% to 24.0% (p<0.01); 95% CI not reported | — | Low | — | 1 studies |
| Relative abundance of Prevotella | synbiotic: 5.28% to 14.4% (p<0.001); placebo: 6.4% to 12.4% (p<0.01); increase in both groups, in the group-specific effect confirmed; 95% CI not reported | — | Low | — | 1 studies |
| Relative abundance of Dialister | synbiotic group: 9.68% to 13.4% (p<0.05); placebo group data not reported for this genus; 95% CI not reported | — | Low | — | 1 studies |
| Beta-diversity composition (phylum level) | similar at baseline between groups; post-intervention between-group comparison qualitative only; in the statistical test or effect size reported for beta-diversity | — | Low | — | 1 studies |
| Dominance of specific species (Collinsella stercoris vs. Bacteroides eggerthi) | Collinsella stercoris dominant in synbiotic group; Bacteroides eggerthi dominant in placebo group at week 12; in the quantitative effect size or p-value reported for this comparison | — | Low | — | 1 studies |
Context
Gut microbiota is a candidate therapeutic target in pediatric obesity, yet controlled trials in this population remain scarce. The obesity-associated microbial profile — elevated F/B ratio, reduced diversity — is potentially modifiable by synbiotics. High-quality data in children are required before clinical recommendations can be made.
What the study showed
In the synbiotic group, F/B ratio fell from 3.54 to 2.75 (p<0.05); in the placebo group, from 4.70 to 3.54 (p<0.05); at week 12, the ratio was lower in the synbiotic vs. placebo group (p<0.05), with no 95% CI reported. Bacteroidetes increased from 18.8% to 24.0% in the synbiotic group (p<0.01). Prevotella increased from 5.28% to 14.4% in the synbiotic group (p<0.001) and from 6.4% to 12.4% in the placebo group (p<0.01), indicating a partially non-specific effect. Alpha diversity (observed OTUs and Chao1) decreased in the synbiotic group after 12 weeks (p<0.001 for both), with no change in the placebo group — an unfavorable direction for this outcome.
How it was done
Double-blind, placebo-controlled RCT (Probesity-2, NCT05162209); 1:1 allocation; 12-week intervention. Fecal samples collected at baseline and week 12, analyzed by detailed metagenomics and bioinformatics. The full text provided does not specify total sample size or complete inclusion/exclusion criteria.
Effect magnitude
F/B ratio dropped 22% in the synbiotic group (3.54→2.75) vs. 25% in placebo (4.70→3.54); the between-group difference at endpoint was statistically significant (p<0.05), but 95% CI and standardized effect sizes were not reported in the available text.
Risk of bias
Total sample size is not stated in the provided text, precluding power assessment; 95% CIs and standardized effect sizes are absent for primary outcomes. Both groups received concurrent dietary and physical activity interventions, making it impossible to isolate the synbiotic effect. The decrease in alpha diversity in the intervention group is a concerning signal not adequately discussed. Formal risk-of-bias assessment (RoB 2 tool) was not applied by the authors. Follow-up limited to 12 weeks with no sustainability assessment.
What this study does NOT prove
This study does not prove that the synbiotic improves metabolic or health outcomes in pediatric obesity, nor that the observed microbial changes are causally beneficial. Findings are not generalizable to children without concurrent dietary and physical activity interventions.
In clinical practice
The tested synbiotic should not be recommended as a standalone microbiota modulator in obese children based on this study. The decrease in alpha diversity in the synbiotic group is clinically relevant and contradicts the benefit narrative. Clinicians should await trials with larger samples, reported CIs, and hard clinical endpoints.
Limitations
Total sample size is not stated in the provided text, precluding power assessment; 95% CIs and standardized effect sizes are absent for primary outcomes. Both groups received concurrent dietary and physical activity interventions, making it impossible to isolate the synbiotic effect. The decrease in alpha diversity in the intervention group is a concerning signal not adequately discussed. Formal risk-of-bias assessment (RoB 2 tool) was not applied by the authors. Follow-up limited to 12 weeks with no sustainability assessment.
What is still missing
Trials with larger samples, ≥6-month follow-up, an arm without dietary/physical activity co-intervention, and hard clinical primary outcomes (BMI-z score, metabolic markers) are needed to establish causality and clinical relevance.
Technical appendix
Version history
- 1.0 · 2026-06-22 — Auto-generated under Evidence Standard v1.0