Bariatric Surgery Alters Oral Microbiome: Evidence From Obese Patients and a Mouse Model

Background Bariatric surgery (BaS) is a safe and effective treatment for severe obesity, yet recent studies suggested that it may impact the gut and oral microbiomes. Oral dysbiosis is associated with an increased risk of oral diseases, including periodontitis and dental caries. However, the effects of BaS on oral health and microbiome changes are poorly understood. Objectives To examine the impact of obesity and BaS on oral health and microbiota in obese patients and an induced experimental periodontitis (EP) obese mouse model. Methods The oral health of pre-BaS, post-BaS (6 months post-surgery), and control volunteers was assessed by scoring gingivitis, caries, and periodontitis. The oral microbiome was analyzed using 16S rRNA Next-Generation sequencing (NGS). Systemic parameters, maxillary bone volume, and oral and fecal microbiome were investigated in male obese C57BL/6 mice with and without EP before and after BaS treatment. Results The study included 36 pre-BaS patients, 14 post-BaS patients, and 56 controls. Distinct oral microbial profiles were noted for each cohort. Pre-BaS patients exhibited higher oral microbial diversity and a greater prevalence of periodontitis-associated bacteria than controls, which further increased post-BaS. Caries- and halitosis-associated bacteria were significantly more abundant after BaS. Similarly, obese mice with EP and that underwent BaS showed elevated oral microbial diversity, paralleling human findings. EP alone significantly reduced gut microbiome diversity, regardless of BaS. Conclusions BaS exacerbates obesity-related microbial dysbiosis, increasing the risk of periodontal and dental diseases. Paradoxically, while BaS improves systemic and cardiometabolic health, it appears to worsen oral outcomes, underscoring the need for integrated medical–dental care and preventive protocols in this population.