Metabolic bone disease manifesting as osteopenia and secondary hyperparathyroidism have been reported after Roux-en-Y gastric bypass surgery due to reduced calcium absorption. The highest concentration of calcium transporters is in the duodenum. Since the ingested food will not pass through the duodenum after a bypass procedure, calcium levels in the blood may decrease, causing secondary hyperparathyroidism, increase in bone turnover, and a decrease in bone mass.