One anastomosis gastric bypass produces considerable weight reduction and resolution of medical complications with an acceptable rate of nutritional deficiencies.

One anastomosis gastric bypass (OAGB) is a relatively novel bypass surgery variant, increasingly used as a primary surgical procedure. A total of 101 patients (mean age 44.7 ± 10.7 years, mean BMI 47.2 ± 6.6 kg/m2) underwent OAGB between 2014 and 2019 in a single institution. Results obtained 6,12 and 24 months postoperatively were compared with the pre-operative values using "Analyse-it software v5.40.2" and Graphpad Prism v9.3 for figures and tables. Data were tested for normality, described as Mean ± SD, compared using paired sample t-test with 5% p-value for significance and 95% confidence interval (CI). A significant body mass index (BMI), haemoglobin A1c (HbA1c) and low-density lipoprotein (LDL) reduction was recorded throughout follow-up period, with greatest improvement seen 2 years after surgery (47.6 ± 22 kg/m2 vs. 29.4 ± 6.4 kg/m2 ,6.7 ± 1.8% vs. 5.5 ± 0.2% and 3.2 ± 1 vs. 2.05 + 0.7 mmol/ l, p < 0.05). The number of glucose-lowering drugs decreased from 1.6 ± 0.9 to 0.3 ± 0.4 at 24-months, p < 0.001. The rates for zinc, ferritin, folate, B12 and vitamin D deficiency at 24-months were: 8.9%,4%, 5.9%, 0% and 3% respectively. OAGB can effectively downstage obesity disease and improve glucose and lipid homeostasis with a low risk for nutritional deficiencies. This study is one of few to report specifically on the frequency and type of nutritional deficiencies following OAGB surgery.