The very nature of gastric bypass surgery disrupts the absorption of vitamins into the body. For one, the area of the small intestine where vitamins are absorbed is no longer used. Secondly, the smaller size of the stomach also affects vitamin digestion in the stomach. Additional vitamins for gastric bypass patients are important to avoid the complications that go along with these deficiencies. Supplemental vitamins and minerals should include Vitamin A, Calcium, Vitamin B12, Vitamin D, Vitamin E, Selenium, Thiamin and Iron. Multivitamins specifically geared toward the needs of bariatric patients are available.