Gastric bypass is a form of weight loss, or bariatric, surgery. In the procedure, the patient's stomach is essentially recreated into a much smaller pouch, thereby allowing a much smaller amount of food to be ingested. Additionally, part of the small intestine is attached to the new stomach pouch. One of the results is a lower absorption of nutrients. Therefore, in order to make up for the reduction in food and nutrient intake, gastric bypass patients should take vitamins to supplement their diet.
Vitamin D is essential to help the body absorb calcium. According to a study reported in the "Journal of Clinical Endocrinology & Metabolism" in July 2008, one year after having gastric bypass, a group of patients were found to have had major decreases in bone density. Adequate amounts of calcium are required to build and maintain strong bones.
In a report published in "The Lancet" in October 2008, the case of a woman who had undergone gastric bypass surgery was cited. About two months after surgery, she was vomiting and extremely dizzy. After a series of tests, they all indicated that the patient had a severe vitamin B1 (or thiamine) deficiency. The woman acknowledged that she had not been taking the recommended dose of vitamins that she'd been given. Accordingly, B1 is essential.
Patients who have undergone gastric bypass surgery are required to take a multivitamin for the rest of their lives, according to the Medical University of South Carolina. It is crucial that the multivitamin contain Vitamins A, D and E, as well as folate.