Extensive studies have shown that breast milk is the best source of nutrition for infants, especially during the first six months, because it fulfills almost all of their nutritional needs. Among the many functional building blocks in breast milk, human milk oligosaccharides (HMOs) have been receiving more attention recently. Furthermore, it is the third most common group of compounds in human milk, and studies have demonstrated the health benefits it provides for infants, including improved nutritional status. HMOs were previously known as the ‘bifidus factor’ due to their ‘bifidogenic’ or prebiotic effects, which enabled the nourishment of the gastrointestinal microbiota. Healthy gastrointestinal microbiota are intestinal health substrates that increase nutrient absorption and reduce the incidence of diarrhea. In addition, HMOs, directly and indirectly, protect infants against infections and strengthen their immune system, leading to a positive energy balance and promoting normal growth. Non-modifiable factors, such as genetics, and modifiable factors (e.g., maternal health, diet, nutritional status, environment) can influence the HMO profile. This review provides an overview of the current understanding of how HMOs can contribute to the prevention and treatment of nutritional issues during exclusive breastfeeding.

Purpose: Human milk oligosaccharides (HMOs) may be genetically determined based on the secretor and Lewis status of the mother. This study aims to determine the HMO profile and the secretor and Lewis gene status of Indonesian lactating mothers. Methods: Baseline data of 120 mother-infant pairs between 0-4 months post-partum obtained from a prospective longitudinal study was used. The concentrations of 2'-fucosyllactose (2’FL), lacto-N-fucopentaose I (LNFP I), lacto-N-tetraose (LNT), lactoN-neotetraose (LNnT), 3'-sialyllactose (3’SL), and 6'-sialyllactose (6’SL) were measured.Genetic analysis was performed for mothers using targeted next-generation sequencing and Sanger sequencing. Wild-type AA with the rs1047781 (A385T) polymorphism was categorized as secretor positive, while heterozygous mutant AT was classified as a weak secretor. The presence of rs28362459 (T59G) heterozygous mutant AC and rs3745635 (G508A) heterozygous mutant CT genes indicated a Lewis negative status, and the absence of these genes indicated a positive status. Subsequently, breast milk was classified into various groups, namely Group 1: Secretor+Lewis+ (Se+Le+), Group 2: Secretor−Lewis+ (Se−Le+), Group 3: Secretor+Lewis− (Se+Le−), and Group 4: Secretor−Lewis− (Se−Le−). Data were analyzed using the Mann–Whitney and Kruskal–Wallis rank tests, and a p-value of 0.05 indicated statistical significance. Results: A total of 58.3% and 41.7% of the samples had positive and weak secretor statuses, respectively. The proportion of those in Group 1 was 85%, while 15% were Group 3.The results showed that only 2'FL significantly differed according to the secretor status (p-value=0.018). Conclusion All Indonesian lactating mothers in this study were secretor positive, and most of them had a Lewis-positive status.