Objective To investigate the therapeutic efficacy and potential mechanisms of fecal microbiota transplantation (FMT) in patients with type 2 diabetes mellitus (T2DM), and to preliminarily identify the traditional Chinese medicine (TCM) syndrome element characteristics of FMT in the treatment of T2DM.

Methods Between March 25, 2023 and September 30, 2024, T2DM patients who met the inclusion and exclusion criteria were enrolled at the Department of Rheumatology and Endocrinology of the Second Affiliated Hospital of Fujian University of Traditional Chinese Medicine. Participants received oral microbiota capsules as an adjunct to metformin therapy. Information obtained by four diagnostic methods of TCM, along with clinical and laboratory parameters, was collected before and after the intervention. Metagenomic sequencing was employed to analyze the gut microbiota, and Spearman correlation analysis was used to explore the relationship between laboratory indicators and differential bacterial genera. According to the post-treatment reduction in glycosylated hemoglobin (HbA1c), patients were categorized into a response (R) group and a non-response (NR) group. Treatment outcomes, safety indicators, gut microbiota changes, and TCM syndrome element features were compared between the two groups.

Results A total of 53 T2DM patients were included in the final analysis, and 30 patients were assigned to R group and 23 to NR group. After treatment, the R group exhibited significant reductions in HbA1c, fasting plasma glucose (FPG), and 2-hour postprandial glucose (2hPG) (P < 0.05 or P < 0.01). The NR group also showed significant decreases in HbA1c and FPG levels P < 0.01 or P < 0.05. Compared with the NR group, after treatment, FPG level in the R group demonstrated significant reductions (P < 0.01). As compared with before treatment, pancreatic islet function demonstrated enhancement in the R group, a significant increase in the 2-hour pastprandial C-peptide (2hC-P) levels in R group (P < 0.05), whereas no marked change was observed in the NR group. Regarding body composition indicators, the R group showed significantly lower waist-hip ratio (WHR), visceral fat (VF), and subcutaneous fat (SF) levels compared with the NR group (P < 0.01). After treatment, the NR group exhibited a significant elevation in aspartate aminotransferase (AST) levels (P < 0.05). Other safety-related indicators fluctuated within normal reference ranges, and no other adverse events, such as diarrhea, fever, or nausea, were reported. Metagenomic sequencing showed that FMT improved the diversity and richness of the gut microbiota, remodeling its overall structure. At the phylum level, the abundance of p_Firmicutes decreased significantly (P < 0.01), while the abundances of p_Bacteroidota and p_Proteobacteria increased significantly (P < 0.01). At the family level, among the 125 identified taxa, the abundances of f_Bacteroidaceae, f_Lactobacillaceae, and f_Sutterellaceae were significantly elevated, whereas six families, including f_Lachnospiraceae, f_Ruminococcaceae, and f_Coriobacteriaceae, were significantly decreased (all P < 0.05). Among the 367 taxa at the genus level, the top 10 differential genera showed significantly increased abundances of g_Bacteroides and g_Sutterella, and significantly decreased abundances in eight genera, including g_Faecalibacterium, g_Ruminococcus, g_Blautia, and g_Collinsella (all P < 0.05). Correlation analysis suggested that the phylum p_Bacillota was positively correlated with improvements in T2DM laboratory parameters, g_norank_f_Prevotellaceae was significantly positively correlated with fasting C-peptide (FC-P) and 2hC-P (P < 0.05). HbA1c demonstrated a significantly positive correlation with g_Blautia and g_Gemmiger (P < 0.05) and a significantly negative correlation with g_Bacteroides and g_Collinsella (P > 0.05). Analysis of syndrome element characteristics revealed that the R group was primarily characterized by pathological patterns of dampness, phlegm, and Yang deficiency. Before treatment, statistically significant reductions in syndrome element scores were observed for dampness, Yang deficiency, spleen, phlegm, Qi deficiency, Qi stagnation, and Yin deficiency (P < 0.01), as well as for heat and liver (P < 0.05). The NR group was mainly featured with Qi deficiency and Yin deficiency. Statistically significant changes in their syndrome element scores after treatment were noted for Qi deficiency (P < 0.01), and for spleen, Qi stagnation, liver, and blood deficiency (P < 0.05). In this group, the score changes for Yang deficiency, Yin deficiency, heat, and dampness were not statistically significant (P > 0.05).

Conclusion The principles of syndrome element differentiation can be effectively applied to predict treatment efficacy and facilitate patient selection for FMT in the treatment of T2DM. Patients with T2DM presented with specific TCM syndrome element characteristics, notably dampness, phlegm, and Yang deficiency, represent a highly responsive population to FMT therapy.