Background Disturbances in the gut microbiome (GM) during the first year of life may contribute to allergy risk. This period is characterized by rapid microbial colonization, influenced by factors like delivery mode and infant feeding practices. This study investigated changes in key GM taxa and fecal metabolites in relation to allergy development, delivery mode, age, and infant feeding practices during the first year of life. Methods In this study, 72 infants, exclusively breastfed for at least 16 weeks and at risk of developing allergies, were followed in their first year during which allergy manifestations were recorded and fecal samples were collected. The samples were subjected to metabolic profiling covering host and microbial metabolites and fluorescent in situ hybridization to quantify Bifidobacterium spp. and the Eubacterium rectale/Clostridium coccoides group. Results Strong age-associated metabolic shifts were observed, particularly in aromatic amino acid metabolites, bile acids, B vitamins, and short and long-chain fatty acids. Introduction of complementary feeding and the cessation of breastfeeding were significantly associated with changes to the fecal metabolome. Delivery mode had a pronounced impact on the metabolome, with differences persisting until 6 months of age. Infants who developed an allergy (n=20) had lower Bifidobacterium spp. and higher polyunsaturated fatty acid levels before the age of 16 weeks. Conclusion This study offers valuable insights into the longitudinal development of the fecal metabolome during infancy. It highlights potential early biomarkers for allergy risk, which could inform future dietary strategies to support gut health and reduce the risk of developing allergies.