Pediatric obesity is associated with an altered gut microbiota and discordant shifts in firmicutes populations

An altered gut microbiota has recently been linked to obesity. However, knowledge about gut microbiota in paediatric obesity is currently very limited. The primary aim of this study was to characterize the composition of the gut microbiota in obese (n=42) and normal-weight (n=36) Italian children between 6 and 16 years of age. Using 16S rRNA gene-targeted sequencing, we evaluated taxa with differential abundance according to weight status and age- and sex-normalized body mass index (BMI z-score). Obesity was associated with an altered gut microbiota, which was characterized by elevated levels of Firmicutes and depleted levels of Bacteroidetes. Correlation network analysis revealed that the gut microbiota of obese children also had increased correlation density and clustering of operational taxonomic units (OTUs). Members of the Bacteroidetes were generally better predictors of BMI z-score and obesity than Firmicutes, which was likely due to discordant responses of Firmicutes OTUs, with some positively and some negatively correlated with BMI z-score. In accordance with these observations, the main metabolites produced by gut bacteria, short chain fatty acids (SCFAs), were significantly higher in obese children, suggesting elevated substrate utilization by the gut microbiota of obese children. Multiple taxa were correlated with SCFA levels, reinforcing the tight link between the microbiota, SCFAs, and obesity. Our results suggest that gut microbiota dysbiosis and elevated fermentation activity may be involved in the etiology of childhood obesity.