BACKGROUND One anastomosis (mini) gastric bypass (OAGB) is believed to be more malabsorptive than Roux-en-Y gastric bypass. A number of patients undergoing this procedure suffer from severe protein-calorie malnutrition requiring revisional surgery. The purpose of this study was to find the magnitude of severe protein-calorie malnutrition requiring revisional surgery after OAGB and any potential relationship with biliopancreatic limb (BPL) length. METHODS A questionnaire-based survey was carried out on the surgeons performing OAGB. Data were further corroborated with the published scientific literature. RESULTS A total of 118 surgeons from thirty countries reported experience with 47,364 OAGB procedures. Overall, 0.37% (138/36,952) of patients needed revisional surgery for malnutrition. The highest percentage of 0.51% (120/23,277) was recorded with formulae using >200 cm of BPL for some patients, and lowest rate of 0% was seen with 150 cm BPL. These data were corroborated by published scientific literature, which has a record of 50 (0.56%) patients needing surgical revision for severe malnutrition after OAGB. CONCLUSIONS A very small number of OAGB patients need surgical correction for severe protein-calorie malnutrition. Highest rates of 0.6% were seen in the hands of surgeons using BPL length of >250 cm for some of their patients, and the lowest rate of 0% was seen with BPL of 150 cm. Future studies are needed to examine the efficacy of a standardised BPL length of 150 cm with OAGB.