Objective To investigate the impact of gut-brain axis interaction on disease condition and prognosis in patients with obesity and type 2 diabetes mellitus (T2DM) following bariatric and metabolic surgery.

Methods Fifty patients with obesity and T2DM who underwent bariatric and metabolic surgery were recruited as study subjects. Serum levels of gastrointestinal peptide hormonesinsulin (Ins), leptin (Lep), glucagon-like peptide-1 (GLP-1), ghrelin (Ghr), glycated hemoglobin (HbA1c), and body mass index (BMI) were compared before and after treatment. Additionally, 16S rRNA amplicon sequencing of fecal samples was performed to determine the composition and abundance of gut microbiota. Pearson's correlation analysis and Spearman rank correlation analysis were used to assess the correlations of serum gastrointestinal peptide hormones, gut microbiota abundance indices with BMI and HbA1c. Patients were followed up for one year, and the occurrence of adverse outcomes was recorded. Multivariate logistic regression analysis was employed to explore influencing factors of the prognosis of patients with obesity and T2DM one year after bariatric and metabolic surgery.

Results Compared with pre-treatment levels, post-treatment BMI, serum HbA1c, and Ghr levels decreased, while serum Ins, Lep, and GLP-1 levels increased (P < 0.05). Post-treatment, gutmicrobiota abundanceindices, including Shannon and Simpson indices, increased significantly compared to pre-treatment levels (P < 0.05). After treatment, the proportions of Firmicutes, Bacteroidetes in the gut microbiota were lower than pre-treatment, but the proportion of Proteobacteria was higher than pre-treatment (P < 0.05). Correlation analysis revealed that serum Ins, Lep, and GLP-1 levels were separately negatively correlated with BMI and HbA1c (P < 0.05), while serum Ghr level was separately positively correlated with BMI and HbA1c (P < 0.05). Both Shannon and Simpson indices were negatively correlated with BMI and HbA1c (P < 0.05). Multivariate Logistic regression analysis showed that serum Lep, serum GLP-1, and Simpson index were protective factors for prognosis in patients with obesity and T2DM after bariatricand metabolic surgery (OR=0.523, 0.417, 0.613, P=0.020, 0.015, 0.026), while serum HbA1c was a risk factor (OR=2.913, P=0.029).

Conclusion Bariatric and metabolicsurgery can regulate gut microbiota composition and gastrointestinal peptide hormone levels in patients with obesity and T2DM, thereby improving disease condition and prognosis through gut-brain axis interaction.