These human milk oligosaccharides (HMOs) are not digestible by host glycosidases and yet are produced in large amounts with highly variable structures by the mother. HMOs appear to have three important functions: prebiotic (stimulation commensal bacteria containing the bacterial glycosidases to deconstruct and consume the HMOs), decoy (structural similarity to the glycans on enterocytes allows HMOs to competitively bind to pathogens), and provision of fucose and sialic acid that appear to be important in host defense and neurodevelopment respectively