This study examines Blastocystis dynamics in 15 individuals undergoing sleeve gastrectomy. Molecular detection involved DNA extraction, RT-PCR, and sequencing, while 16S rRNA sequencing via Illumina MiSeq analyzed the intestinal microbiome. Statistical analysis through SPSS considered a significance level of p <
0.05. Postoperative colonization of Blastocystis was observed in previously negative individuals, revealing subtypes and shifts in microbial taxa. Blastocystis-positive participants post-bariatric surgery showed a significant increase in Lachnospira, alongside higher abundances of Bacteroides, Oscillospira, Barnesiellaceae, and Rikenellaceae, with reduced Lactobacillus levels compared to Blastocystis-negative individuals. Collective analysis highlighted higher Clostridiales and RF32 in Blastocystis-positive post-surgery individuals, coupled with decreased Enterobacteriaceae. The study challenges previous notions, suggesting a complex interplay between Blastocystis, morbid obesity, and bariatric surgery. Despite limitations, including small sample sizes and absent gut microbiome diversity comparisons, this pioneering research calls for further investigation into the intricate mechanisms and implications for metabolic health. This study is registered at clinicaltrials.gov (NCT05085769).