Iron-Fortification and Inulin Supplementation in Early-Infancy: Evaluating the Impact on Iron Metabolism and Trace Mineral Status in a Piglet Model

Background Infant formula in the U.S. contains abundant iron, raising health concerns about excess iron intake in early infancy. Objectives Using a piglet model, we explored the impact of high iron fortification and pre- or synbiotic supplementation on iron homeostasis and trace mineral bioavailability. Methods Twenty-four piglets were stratified and randomly assigned to treatments on postnatal day (PD) 2. Piglets were individually housed and received an iron-adequate milk (AI), a high-iron milk (HI), the HI milk supplemented with 5% inulin (HIP), or the HIP milk with an oral gavage of Ligilactobacillus agilis YZ050, an inulin-fermenting strain, every third day (HIS). Milk was provided in 14 meals daily, mimicking formula feeding in infants. Fecal consistency score and body weight were recorded daily or every other day. Blood and feces were sampled weekly, and tissues collected on PD 29. Data were analyzed using mixed model ANOVA with repeated measures whenever necessary. Results Diet did not affect growth. High-iron milk increased hemoglobin, hematocrit and serum iron compared to AI. Despite marginal adequacy, AI milk upregulated iron transporter genes and maintained satisfactory iron status in most pigs. High-iron milk upregulated hepcidin gene in liver, caused pronounced tissue iron deposition, and markedly increased colonic and fecal iron. Inulin supplementation, regardless of L. agilis YZ050, not only attenuated hepatic iron overload but also decreased colonic and fecal iron without altering pH or iron regulatory genes. The HI milk lowered zinc (Zn) and copper (Cu) in duodenum and liver compared to AI, while HIP and HIS further decreased Zn and Cu in liver and diminished the increase of colonic and fecal trace minerals caused by HI. Conclusion Early-infancy excessive iron fortification causes iron overload and compromises Zn and Cu absorption. Inulin decreases trace mineral absorption likely through enhancing gut peristalsis and stool frequency.