Roux-en-Y gastric bypass (RYGB) is one of the most performed bariatric surgical techniques. However, RYGB commonly results, as side effects, in nutritional deficiencies. This study aimed to examine changes in the expression of vitamin A pathway encoding genes in the gastrointestinal tract (GI) and to evaluate the potential mechanisms associated with hypovitaminosis A after RYGB. Intestinal biopsies were obtained through double-balloon endoscopy in 20 women with obesity (age 46.9±6.2 years; body mass index [BMI] 46.5±5.3 kg/m² [mean±SD]) before and three months after RYGB (BMI, 38.2±4.2 kg/m²). Intestinal mucosal gene microarray analyses were performed in samples using a Human GeneChip 1.0 ST array (Affymetrix). Vitamin A intake was assessed from 7-day food records and serum retinol levels were evaluated by electrochemiluminescence immunoassay. Our results showed the following genes with significant downregulation (p≤0.05): LIPF (−0.60), NPC1L1 (−0.71), BCO1 (−0.45), and RBP4 (−0.13) in the duodenum; CD36 (−0.33), and ISX (−0.43) in the jejunum and BCO1 (−0.29) in the ileum. No significant changes in vitamin A intake were found (784±694 retinol equivalents [RE] pre-operative vs. 809±753 RE post-operative [mean±SD]). Although patients were routinely supplemented with 3500 international units IU/day (equivalent to 1050 μg RE/day) of oral retinol palmitate, serum concentrations were lower in the post-operative when compared to pre-operative period (0.35±0.14 μg/L vs. 0.52±0.33 μg/L, respectively – P=0.07), both within the normal range. After RYGB, the simultaneous change in expression of GI genes, may impair carotenoid metabolism in the enterocytes, formation of nascent chylomicrons and transport of retinol, resulting in lower availability of vitamin A.

Background: Metabolic and bariatric surgery is an effective obesity treatment. One anastomosis gastric bypass (OAGB) has emerged as an alternative to Roux-en-Y gastric bypass (RYGB); however, evidence regarding its postoperative nutritional outcomes remains limited. Objective: To compare food tolerance, gastrointestinal symptoms, and nutritional status between OAGB and RYGB one year after surgery. Methods: This retrospective, observational, comparative study included 46 patients (16 OAGB and 30 RYGB). Weight loss, laboratory parameters, dietary intake, food tolerance, and gastrointestinal symptoms were evaluated one year postoperatively. Linear regression models were adjusted for relevant confounding variables, including age, sex, and baseline values when appropriate. Results: The percentage of total weight loss (29.55% vs 26.32%) and excess weight loss (63.36% vs 58.29%) were similar between RYGB and OAGB groups (P>0.05). A high prevalence of vitamin D deficiency was observed in both groups (RYGB: 82% vs. OAGB: 92%). Elevated parathyroid hormone levels were more frequent in the OAGB group (75% vs 50%), although the difference was not statistically significant. OAGB patients showed numerically lower serum iron and reduced transferrin saturation; however, none of the patients developed anemia. Mean protein intake met the recommended levels in both groups, whereas fiber intake was below the minimum recommended level. OAGB patients presented significantly lower gastrointestinal symptom scores for diarrhea, indigestion, and total score (P<0.05). Food tolerance was satisfactory and similar between groups. Conclusion: Under structured multidisciplinary follow-up, OAGB and RYGB demonstrated comparable nutritional outcomes. OAGB appears to be a nutritionally safe alternative at one year of follow-up, with the need for ongoing monitoring of iron and vitamin D status.