This study investigates the impact of Roux-en-Y gastric bypass (RYGB) surgery on the gut microbiota of obese individuals and its association with metabolic and low-grade inflammation markers. The research involved 13 lean control subjects and 30 obese individuals (including 7 with type 2 diabetes) analyzed before, 3 months, and 6 months after RYGB. Key findings include: 1) The Bacteroides/Prevotella group was lower in obese individuals at baseline but increased after surgery, negatively correlated with corpulence. 2) Escherichia coli increased at 3 months and inversely correlated with fat mass and leptin levels. 3) Lactic acid bacteria and Bifidobacterium decreased at 3 months. 4) Faecalibacterium prausnitzii was lower in diabetic subjects and negatively associated with inflammatory markers. The study suggests that gut microbiota rapidly adapts to the starvation-like state induced by RYGB, with F. prausnitzii directly linked to reduced low-grade inflammation in obesity and diabetes, independent of calorie intake. Obesity is associated with low-grade inflammation and altered gut microbiota, which may contribute to metabolic disorders. RYGB leads to significant improvements in metabolic and inflammatory markers, possibly due to changes in gut microbiota. The study highlights the role of gut microbiota in energy harvesting, body fat storage, and inflammation. The results indicate that RYGB induces rapid microbiota changes, with F. prausnitzii playing a key role in reducing inflammation. The study also explores the relationship between gut microbiota composition and clinical parameters, showing that F. prausnitzii is negatively correlated with inflammatory markers. The findings suggest that F. prausnitzii may be a therapeutic target for improving inflammation, glucose tolerance, and insulin sensitivity in obesity and diabetes. The study underscores the importance of understanding gut microbiota changes in the context of bariatric surgery and their potential impact on metabolic health.This study investigates the impact of Roux-en-Y gastric bypass (RYGB) surgery on the gut microbiota of obese individuals and its association with metabolic and low-grade inflammation markers. The research involved 13 lean control subjects and 30 obese individuals (including 7 with type 2 diabetes) analyzed before, 3 months, and 6 months after RYGB. Key findings include: 1) The Bacteroides/Prevotella group was lower in obese individuals at baseline but increased after surgery, negatively correlated with corpulence. 2) Escherichia coli increased at 3 months and inversely correlated with fat mass and leptin levels. 3) Lactic acid bacteria and Bifidobacterium decreased at 3 months. 4) Faecalibacterium prausnitzii was lower in diabetic subjects and negatively associated with inflammatory markers. The study suggests that gut microbiota rapidly adapts to the starvation-like state induced by RYGB, with F. prausnitzii directly linked to reduced low-grade inflammation in obesity and diabetes, independent of calorie intake. Obesity is associated with low-grade inflammation and altered gut microbiota, which may contribute to metabolic disorders. RYGB leads to significant improvements in metabolic and inflammatory markers, possibly due to changes in gut microbiota. The study highlights the role of gut microbiota in energy harvesting, body fat storage, and inflammation. The results indicate that RYGB induces rapid microbiota changes, with F. prausnitzii playing a key role in reducing inflammation. The study also explores the relationship between gut microbiota composition and clinical parameters, showing that F. prausnitzii is negatively correlated with inflammatory markers. The findings suggest that F. prausnitzii may be a therapeutic target for improving inflammation, glucose tolerance, and insulin sensitivity in obesity and diabetes. The study underscores the importance of understanding gut microbiota changes in the context of bariatric surgery and their potential impact on metabolic health.