One anastomosis gastric bypass (OAGB) is an emerging bariatric procedure, yet data on its effect on the gastrointestinal tract are lacking. This study sought to evaluate the incidence of small-intestinal bacterial overgrowth (SIBO) following OAGB; explore its effect on nutritional, gastrointestinal, and weight outcomes; and assess post-OABG occurrence of pancreatic exocrine insufficiency (PEI) and altered gut microbiota composition. A prospective pilot cohort study of patients who underwent primary-OAGB surgery is here reported. The pre-surgical and 6-months-post-surgery measurements included anthropometrics, glucose breath-tests, biochemical tests, gastrointestinal symptoms, quality-of-life, dietary intake, and fecal sample collection. Thirty-two patients (50% females, 44.5 ± 12.3 years) participated in this study, and 29 attended the 6-month follow-up visit. The mean excess weight loss at 6 months post-OAGB was 67.8 ± 21.2%. The glucose breath-test was negative in all pre-surgery and positive in 37.0% at 6 months (p = 0.004). Positive glucose breath-test was associated with lower reported dietary intake and folate levels and higher vitamin A deficiency rates (p ≤ 0.036). Fecal elastase-1 test (FE1) was negative for all pre-surgery and positive in 26.1% at 6 months (p = 0.500). Both alpha and beta diversity decreased at 6 months post-surgery compared to pre-surgery (p ≤ 0.026). Relatively high incidences of SIBO and PEI were observed at 6 months post-OAGB, which may explain some gastrointestinal symptoms and nutritional deficiencies.

Given the health benefits of carotenoids, it is crucial to evaluate their levels in patients undergoing malabsorptive procedures like one anastomosis gastric bypass (OAGB). This study aimed to assess serum carotenoid levels before and 6 months following OAGB. Prospectively collected data from patients who underwent primary OAGB were analyzed. Data included anthropometrics, dietary intake assessments, and biochemical tests. Serum samples were analyzed for lipid profile and serum carotenoids, including lutein, zeaxanthin, α-carotene, β-carotene, phytofluene, ζ-carotene, and lycopene. Data from 27 patients (median age 47.0 years and 55.6% female) were available before and 6 months post-OAGB. The median pre-surgical BMI was 39.5 kg/m², and the median excess weight loss at 6 months post-surgery was 63.9%. Significant decreases in all carotenoid levels were observed over time (p < 0.001 for all). A median relative decline of 65.1% in absolute total carotenoid levels and 12.7% in total cholesterol levels were found. No associations were observed between changes in clinical outcomes and carotenoid levels during the study period. This study reveals significant decreases in carotenoid levels within the first 6 months following OAGB. Nutritional intervention studies are needed to explore how incorporating carotenoid-rich foods affects post-surgery carotenoid levels and clinical outcomes.