Probiotics After Metabolic and Bariatric Surgery: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background/Objectives: Patients undergoing metabolic and bariatric surgery (MBS) are at risk of micronutrient deficiencies and gut dysbiosis. Probiotics (such as Lactobacillus, Bifidobacterium) have been proposed as adjunct therapy to optimize postoperative outcomes. This review aimed to evaluate the effect of postoperative probiotic supplementation on anthropometric, metabolic, inflammatory, and micronutrient outcomes in MBS patients. Methods: Nine electronic databases were systematically searched, including PubMed, Web of Science, Cochrane Library, Google Scholar, Popline, Global Health Library, Virtual Health Library, New York Academy of Medicine, and OpenGrey, from inception through October 2024. Only randomized controlled trials (RCTs) were included. The Cochrane Collaboration risk-off-bias tool was used for quality assessment. Meta-analyses were performed using Comprehensive Meta-Analysis software version 2. Fixed-effects or random-effects models based on heterogeneity (I2 threshold: 50%) were applied. Mean differences (MD) and 95% confidence intervals (CI) were calculated for all continuous variables. Results: Thirteen RCTs encompassing 666 patients (probiotics group: n = 344; control group: n = 322) were included. Incomplete outcome data represented the most prevalent high-risk domain (23%). Probiotic supplementation was associated with significantly improved serum vitamin D (MD: 25.32 nmol/L, 95% CI: 6.96–43.67, p = 0.007) and vitamin B12 levels (MD: 39.36 pg/mL, 95% CI: 1.88–76.84, p = 0.04). No statistically significant differences were observed in anthropometric outcomes (%EWL, BMI, weight, or waist circumference), lipid profile, glycemic indices, or inflammatory markers (TNF-α, IL-6, CRP). Conclusions: Postoperative probiotic supplementation may significantly improve vitamin D and B12 levels in patients undergoing MBS, suggesting a supportive role in mitigating micronutrient deficiencies. However, these findings should be interpreted with caution due to substantial heterogeneity across studies. Probiotics did not significantly affect weight loss, metabolic parameters, or inflammatory markers. Clinicians may consider probiotics as an adjunct strategy to support micronutrient status in at-risk postoperative patients. Large-scale, strain-specific trials incorporating standardized dietary control and microbiome profiling are warranted.