The Roux-en-Y Gastric Bypass has been associated with very few long-term complications. Reported complications include iron deficiency anemia, vitamin and mineral deficiencies, dehydration, persistent vomiting, and a dumping syndrome.

Iron deficiency anemia: Iron deficiency anemia develops partly due to decreased nutrient intake and partly due to malabsorption of iron. Iron absorption is facilitated by gastric acid and the small pouch produces little acid. Furthermore, iron is predominantly absorbed in the duodenum and proximal jejunum and these areas are bypassed by the surgery. Usual supplementation is Niferex-150 Forte, taken three times a day, and patients must be monitored for a microcytic anemia and decreasing serum iron concentrations.

Vitamin deficiencies: Most vitamin deficiencies can be avoided with daily oral supplementation. However, vitamin B-12 must be supplemented with intramuscular injections every six months or a daily supplemental tablet. For this vitamin to be absorbed from oral intake, it must combine with a protein secreted by the stomach called intrinsic factor. This protein is produced mainly in the bypassed portion of the stomach and therefore will no longer mix with any oral intake. Without intramuscular injections, Vitamin B-12 deficiency has been reported in from 25 to 70 percent of patients following gastric bypass. To avoid catastrophic complications of B-12 deficiency, 1,000 units IM vitamin B-12 should be given every six months.

Mineral abnormalities: Hypocalcemia will occur in all patients without proper supplementation. To be absorbed from dietary intake, calcium must be modified by the action of acid in the stomach. As the small gastric pouch makes little if any acid, dietary calcium will not be absorbed and a calcium deficiency will develop leading to bone demineralization and potential bone fractures. Supplementation with oral calcium as calcium citrate, which does not require acidification for absorption, is completely effective. Usual daily recommendations are from 800 to 1,200 mg calcium.

Dehydration: Dehydration can occur, especially with exposure to dry hot days. Once dehydrated, patients have a significant difficulty catching up and intravenous supplementation is occasionally necessary. Patients should be encouraged to travel with bottles of water and drink throughout the day during hot summer days.