Pediatric obesity has more than doubled in children and tripled in adolescents over the past 30 years. Recent findings demonstrate that differences in energy harvesting bacteria promote obesity in the host and appear to be influenced by early life factors such as mode of delivery, maternal obesity, and breastfeeding. The goal of this proposal is to leverage untargeted metabolomics to investigate how human milk impacts the infant gut microbiome during the first 12-months of life and identify the microbe-host interactions that mediate the protective role of breastfeeding on infant adiposity. The results of this exploratory study will create an data-driven plan to recruit pregnant women into clinical microbiome studies and identify human milk compounds that stabilize a healthy infant microbiome and are associated with infant growth during a critical window of development.