The Impact of Bariatric Surgery on Gut Microbiota Composition and Diversity: A Longitudinal Analysis Using 16S rRNA Sequencing

Bariatric surgery is considered the most effective treatment for obesity and its associated metabolic disorders, yet the underlying mechanisms are only partially understood. Evidence suggests that the gut microbiota plays an important role in metabolic regulation and can be significantly altered by bariatric and metabolic procedures. This prospective, single-center study aimed to evaluate the dynamic changes in the gut microbiota composition and diversity in obese patients undergoing two types of bariatric surgery: laparoscopic sleeve gastrectomy (LSG) and Roux-en-Y gastric bypass (RYGB). Fecal samples were collected at three time points-before surgery (T0), and at 3 (T3) and 6 months (T6) postoperatively-and analyzed using 16S rRNA gene sequencing targeting the V3-V4 regions with Illumina technology. Significant shifts in microbial diversity and structure were observed over time, indicating a trend toward microbiota normalization post-surgery. Notable changes included a reduction in the <i>Firmicutes</i>/<i>Bacteroidetes</i> ratio and increased relative abundance of <i>Actinobacteria</i>, <i>Proteobacteria</i>, and <i>Verrucomicrobia</i>. These alterations occurred in parallel with improvements in body mass index (BMI) and metabolic parameters. Our findings suggest that bariatric surgery induces favorable and sustained modifications in the gut microbiota, which may contribute to its therapeutic effects in obesity management.