Breast milk
Human breast milk contains unique and highly diverse human milk oligosaccharides. These oligosaccharides are considered to be a "Bifidus Factor" because they form highly desired intestinal bacteria; it is for this reason that baby formula contains added oligosaccharides in order to help build a child's immune system. Studies showed that infants, who were bottled fed, lacked intestinal colonization of bifidobacteria. This lack of bacteria made the babies susceptible to other infectious bacteria and ailments. The infants who were breast fed had higher concentration of the bacteria and their vulnerability too infections was significantly lower. Breast milk had high amounts of oligosaccharides. As, a result, oligosaccharides were added to milk formula. This method worked and the colonization of bifidobacteria leveled. This suggested that the oligosaccharides found in human milk were candidates for the bifidus factor.