Bioavailability of Human Milk Oligosaccharides in Healthy Adults

Human milk oligosaccharides (HMOs) have been associated with beneficial health outcomes in breastfed infants, therefore they were investigated intensively within recent years. HMOs support the establishment of a "balanced" intestinal microbiome by acting as both a prebiotic and as a specific antimicrobial. In vitro work has demonstrated that HMOs are resistant to hydrolysis by salivary, pancreatic, and brush-border enzymes, as well as to low gastric pH values enzymes. Consequently, HMOs are mostly resistant to digestion and reach the colon unmodified, where they are available for selective utilisation by certain bacteria. Microbial utilisation results in the formation of microbial metabolites, which are associated with local and systemic effects. Simultaneously, HMOs have bacteriostatic effects and directly limit the growth of potential pathogens. Moreover, they serve as antiadhesives, mimicking intestinal epithelial cell surface receptors to which pathogenic microbes attach, thus acting as a decoy receptor. Additionally, it is suggested that HMOs exert effects independent of the microbiome, by modulating cell recognition and cell signalling. These include interactions with immune cells, thereby modulating the development and responses of the immune system, the maturation of the intestinal glycocalyx, and the promotion of neurodevelopment and cognitive functions. A prerequisite for systemic effects is that HMOs are absorbed and can enter the blood circulation, thus making them potentially available at the systemic level. In order to understand the underlying mechanisms for HMO-mediated, microbe-independent effects, information regarding absorption, metabolisation, and excretion is needed and will be investigated in this study.