4. Discussion
gastrointestinal tract
SECONDARY
In the present study, we characterized circulating plasma metabolites in breastfed infants relative to infants who were fed one of multiple formula preparations that differed only in their oligosaccharide content. Our data demonstrate that there are multiple differences in circulating metabolites between breastfed infants and infants who were exclusively fed control infant formula (Metabolomics is a growing field of research utilizing high throughput liquid and gas chromatography, mass spectrometry, and nuclear magnetic resonance techniques to independently quantify and analyze vast numbers of unique metabolites in biological samples [Importantly, the large study cohort and range of metabolites measured have facilitated insights into the metabolic differences between the metabolism of breastfed and formula-fed infants. Given the large number of differentially expressed metabolites that we observed, we applied Gene Set Enrichment Analysis (GSEA) [The addition of human milk oligosaccharides (HMOs) is perhaps the most significant recent innovation in infant formula. New methods of production have enabled the cost-effective fortification of some infant formulas with oligosaccharides that are biochemically identical to those that occur in nature [The differences in metabolite profiles between infants fed control formula and those fed 2′-FL fortified formula extended beyond 2′-FL and its immediate catabolic products fucose and lactose (Other metabolites associated with microbial activity were elevated in infants fed 2′-FL fortified formula. We applied GSEA to analyze the coordinated regulation of metabolites within known metabolic pathways and found that 2′-FL fortification was associated with a significant increase in bile acid metabolism (We conducted an extensive characterization of differentially expressed secondary bile acids in breastfed infants relative to infants fed the control formula (The absence of data on the composition of the fecal microbiota and fecal secondary bile acids in these study participants is a significant limitation of this study. Given the known prebiotic activity of HMOs and 2′-FL in particular [The physiologic significance of secondary bile acids has undergone significant reevaluation in recent years. Emerging pre-clinical studies have demonstrated that these microbe-derived metabolites play a key role in regulating systemic immunity [In summary, the present study demonstrates that fortification of infant formula with the HMO 2′-FL results in the dose-dependent restoration of certain metabolites derived from microbial activity in the gastrointestinal tract, particularly secondary bile acids. These secondary bile acids play a putative role in the development and maintenance of immune homeostasis [