design: Fecal samples (13 g) were self-collected using sterile kits and transported on dry ice to the Chengdu CDC, where they were stored at 80. All samples were subsequently transferred in a single batch to Tsingke Biotechnology Co., Ltd. for microbial community profiling via 16S rRNA gene sequencing. Sequencing was conducted on the Illumina NovaSeq platform, targeting the V3V4 region with primers 5-ACTCCTACGGGAGGCAGCA-3 and 5-GGACTACHVGGGTWTCTAAT-3.