Health Canada recommends exclusive breastfeeding (EBF) until 6 months followed by introducing iron-rich complementary foods (CFs) such as iron-fortified cereal and meat to prevent iron deficiency (ID). There is a concern that consumption of CFs with high iron dose may predispose infants to inflammation through reactive oxygen species (ROS) generation in their intestinal tract. The nutrient intake from these recommended first CFs had not been assessed in terms of meeting the daily requirements. Therefore the aim of this study was to assess if the recommended CFs are safe from a free radical and inflammatory perspective and to assess these CFs in relation to socio-demographic characteristics, feeding patterns, nutrient intake, iron status and growth. Eighty-seven EBF infants were randomly assigned to receive one of the following: iron-fortified cereal (Cer), iron-fortified cereal with fruit (Cer+Fr), meat (M). Urine and stool samples were collected before and after introduction of CFs to assess the following markers: urinary F2-Isoprostanes, fecal ROS, fecal iron and fecal calprotectin. Blood was collected from 18 infants to measure iron parameters. Socio-demographic characteristics and feeding patterns were obtained using questionnaires. Nutrient intake was collected using 3-day dietary records. There are maternal factors that were associated with selected feeding patterns. Nutrient intake was only adequate when provided by both breast milk and CFs. Plasma ferritin decreased over time in all groups (p = 0.04). Infants in M group had lower fecal iron than infants in Cer and Cer+Fr groups (p < 0.001, p = 0.014, respectively). An increase in fecal ROS formation (p < 0.002) after the introduction of CFs was observed. There are maternal socio-demographic factors such as lower parity and lower BMI that need to be targeted in the future to optimize feeding time, type and frequency. Infants with EBF may be at risk of developing ID despite the provision of iron-rich CFs. Untargeted iron fortification may result in untoward effects including ROS generation in the infant’s intestinal tract. In future, if these findings are further confirmed in EBF and formula-fed infants, reconsidering the strategies of iron fortifications to both meet infants’ requirements and minimizing oxidative stress maybe warranted. / October 2015