Composite fiber remodels gut microbiota and shows a trend of alleviating dyspepsia in adolescents with functional dyspepsia: a 16S rRNA pilot study.

BACKGROUND: Adolescent functional dyspepsia (FD) is highly prevalent and closely linked to intestinal microbiota imbalance. Dietary fiber exerts prebiotic effects by regulating gut microbiota, but targeted studies investigating whether composite fiber can modulate gut microbiota and alleviate dyspeptic symptoms in adolescent FD patients remain scarce. This pilot trial aimed to explore the gut microbial regulatory characteristics and symptomatic improvement trend of standardized composite fiber supplementation. METHODS: Thirty-two adolescents with FD were enrolled in a 28-day double-blind, placebo-controlled pilot trial (treatment group: n = 15, 15 g/d composite fiber; control group: n = 17, isoenergetic maltodextrin). Fecal samples were collected post-intervention for 16S rRNA V3-V4 region sequencing. Microbial functional potential was predicted via PICRUSt1, and Fisher's exact conditional MLE was adopted to compare the binary symptom improvement rates. RESULTS: Composite fiber elevated all α-diversity indices (FDR < 0.05) and separated gut communities (weighted UniFrac PERMANOVA: F = 68.3, R2 = 0.237, p = 0.018), independent of demographics. The intervention was associated with an increased abundance of Akkermansia, Romboutsia, and [Eubacterium]_coprostanoligenes_group, while being associated with a reduction in [Ruminococcus]_gnavus_group and Veillonella. Notably, cross-sectional FD case-control studies reported contradictory shifts of these genera, and microbial responses to intervention show prominent context-dependent heterogeneity across published research. PICRUSt1-based functional prediction suggested significant upregulation of steroid and flavonoid biosynthesis pathways in the treatment group. The symptom improvement rate was numerically higher in the treatment group (66.7% vs. 47.1%), although this difference was not statistically significant (p = 0.3075, OR = 2.19, 95% CI: 0.44-12.15). CONCLUSION: Composite fiber intervention reshapes gut microbial diversity, community structure and predicted metabolic functional profiles in adolescents with FD, alongside a non-significant numerical trend toward the alleviation of dyspeptic discomfort. Owing to substantial inter-study heterogeneity and context-dependent microbial responses, the observed genus-level alterations cannot be unequivocally characterized as uniformly beneficial outcomes, nor can direct causal relationships between single microbial taxa and clinical symptom improvement be inferred, as formal mediation analyses were not performed. This pilot study provides preliminary microbiological evidence for a fiber-based non-pharmacological intervention. Large multi-center trials combining multi-omics datasets and formal mediation analysis are required to validate clinical efficacy and untangle complex microbiota-symptom associations.