Abstract

Breast milk is a complex food, a rich source of nutrients that nourishes the newborn in the first months of life. Breastfeeding extends the intimate bond between a mother and her infant after birth, and it is regarded by the WHO as “the normal way of providing young infants the nutrients they need for healthy growth and development.” Exclusive breastfeeding is recommended for the first six months of age, and thereafter it should be complemented with solid foods for two years (Gartner et al., 2005; Kramer and Kakuma, 2012). The health benefits associated with breastfeeding are multifold. Breast-fed infants have lower infection rates, diarrhea and asthma, in addition to decreased mortality (Shamir, 2016). Moreover, some of these effects can last beyond childhood. Evidence suggests that obesity, allergies, and inflammatory diseases have a lower incidence later in life in breast-fed infants (Horta et al., 2015; Le Huerou-Luron et al., 2010). Even cognitive development appears improved in breast-fed infants (Victora et al., 2015). In addition to essential nutrients such as lactose and fatty acids, breast milk contains a constellation of bioactive molecules, which play critical roles in infant development and protection (Hennet and Borsig, 2016). Bioactive molecules in breast milk are complex and dynamic, making their incorporation in infant formula very difficult to achieve (Cicero et al., 2016; Hill and Newburg, 2015). One of the most remarkable ways that breast milk promotes infant health is by guiding the proper assembly and activity of the gut microbiome (Lemas et al., 2016). This large community of microorganisms starts to assemble at the same time than the newborn is breast-fed. Human milk oligosaccharides (HMO) are present in large concentrations in breast milk and arrive unmodified in the infant colon. Among other roles, they program a microbiome dominated by beneficial gut microbes, especially from the genus Bifidobacterium. In turn, the presence of these microorganisms is regarded as beneficial. Their increased acid production protects the infant against pathogens and they are able to regulate host homeostasis (Ruiz et al., 2016). Advances in glycobiology and genomics have shown that these microorganisms deploy several molecular strategies for utilizing these complex carbohydrates, providing a rationale for their adaptations to the infant gut environment. In this chapter, we discuss recent advances regarding the role of HMO in promoting health through modulation of the infant gut microbiome, with a focus on the molecular structures and strategies deployed by gut microbes to access the energetic content of breast milk.