 Following an overnight fast, subjects will come to the clinical research center. An intravenous catheter will be inserted to collect blood samples. Before the oral administration, blood samples will be collected for the determination of the serum concentration of different iron status markers. The volunteers will receive first an ironIIsulfate supplement, followed by a Fe-chelate supplement at least 7 days between both supplements. After the administration of the supplement, blood samples will be taken at various time points to determine the amount of iron absorption and to investigate if there are any changes in the iron metabolism at 15, 30, 60, 90 minutes and 2; 2.5; 3; 3.5; 4 and 5 hours after oral administration. There will be a one-week washout period between the tests with each iron supplement. The volunteers will be asked to repeat the test before surgery and 1, 3, 6 and 12 months after surgery for each iron supplement. 