Iron absorption from differently labelled iron-fortified maize-based test meals will be measured in 55 infants. At baseline a venipuncture blood sample will be collected from all infants for the determination of the following iron and inflammation status parameters: hemoglobin (Hb), plasma ferritin (PF), soluble transferrin receptor (sTfR), C-reactive protein (CRP) and alpha-1-acid glycoprotein (AGP), and anti-oligosaccharide immunoglobulins. Anthropometrics will be measured; demographics, the medical history and the feeding habits will be assessed using a questionnaire. A breast milk sample from all mothers will be collected for determination of HMO profile and maternal secretor status. After baseline, 30 infants will consume three different test meals on alternate days (day 1, day 3, and day 5) and 25 infants will consume two different test meals on alternate test meal days (day 1, day 3 and day 5). The order of consumption of the three test meals will be randomly assigned. Test meal A will contain 5 mg of iron as ferrous fumarate given as 2.5 mg Fe-56 and 2.5 mg Fe-54 (control test meal). Test meal B will contain 5 mg of iron as ferrous fumarate given as 2.5 mg Fe-56 and 2.5 mg Fe-58 and 4 g of GOS-75 (≈ 3 g GOS) (GOS test meal).Test meal C will contain 5 mg of iron as ferrous fumarate given as 2.5 mg Fe-56 and 2.5 mg Fe-57 and 2.0 g 2'-fucosyllactose (2'-FL) and 1.0 g lacto-N-neotetraose (LNnT) (HMO test meal). The test meals will be based on maize porridge, consisting of refined maize flour, sugar and mineral water, and will be administered between 0700 and 0900. Overnight, only breast milk will be allowed to the infant and no breast milk and no other food will be given at least 3 h before test meal administration. Test meals plus mineral water will be consumed completely in the presence of the investigators, and the infant will not be allowed to eat or drink for 2 h after the test meal. Fourteen days after the third test meal administration (day 17 and 19, respectively) a whole blood sample will be collected by venipuncture for analysis of the ratios of the different molecular weight iron incorporation into red blood cells and determination of iron and inflammation status (Hb, PF, sTfR, CRP and AGP). Furthermore, anthropometrics and some parts of the baseline questionnaire will be repeated.

At endpoint (day 17 and 19, respectively), if the infant will be diagnosed with iron-deficiency anemia (Hb concentration below 110 g/l and low red blood cells mean corpuscular volume), the caregiver will be instructed to give the infant 4mg/kg iron in the form of oral syrup, daily. Compliance during the follow-up will be assessed by weighting the iron syrup containers before and after 14 days of treatment with the iron syrup. Collection of fecal samples will be performed over 3 time periods of 72h each. The first time period will start the 3 days prior of beginning of oral iron supplementation, the second will take place on day 4, 5 and 6 of oral iron supplementation and the last on day 15, 16 and 17 of oral iron supplementation. A venepuncture blood sample will be collected in the morning after the last day of fecal sample collection (day 18 of oral iron supplementation). Furthermore, some parts of the baseline questionnaire will be repeated. Adverse events (AEs) will be assessed throughout the entire study period.