Vitamin B12 deficiency often occurs after bariatric surgery. On the one hand, this is because the patient eats less meat (which is the major source of vitamin B12). On the other hand, it is because the protein 'intrinsic factor', which is produced in the stomach and is necessary for the absorption of vitamin B12, is absent in bariatric patients. The addition of intrinsic factor (IF) to Bariatric Advantage Vitamin B12 I.F. ensures the optimal absorption of vitamin B12.