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Today the WHO Growth Chart Standards, based on the growth of breastfed infants, are used. These growth curves solve the problem of the deviating observations for breastfed compared to non-breastfed infants using previous growth charts. Presently it is not clear how the mother's diet, especially the fat intake, influences the growth of the offspring. Animal experiments indicate that a low intake of n-3 polyunsaturated fatty acids via the milk may have short- and long-term negative consequences. There is limited information in man. It has been suggested that the mammary glands may have phylogenetically originated from glands providing innate immunity, later developing capacities for providing nutrition. This would agree with the fact that human milk contains so many major components which do not primarily function as nutrients, but seem to protect nutrition and growth. Lactoferrin, oligosaccharides, glycoproteins, secretory IgA antibodies, alpha-lactalbumin and the antisecretory factor have such functions.

The newborn has an immune system, very limited in size at birth and its postnatal expansion and maturation takes time. In the meantime the transplacental IgG antibodies from the mother play an important role for the protection of the infant. However, these antibodies act in tissues and induce inflammation and are energy-consuming. In contrast, the milk secretory IgA antibodies stop microbes already on the mucosa preventing infection, tissue engagement and energy loss. In addition, the milk contains many protective factors such as lactoferrin and oligosacharides functioning as analogues for microbial receptors preventing mucosal attachment, the initial step of most infections. As a result, breast-feeding significantly reduces the risk of neonatal septicemia, respiratory tract infections, otitis media, diarrhea, urinary tract infections, infection-induced wheezing and necrotizing enterocolitis. Via several mechanisms it seems that human milk can actively stimulate the immune system of the breast-fed infant. This reduces the risk of infections like otitis media, respiratory tract infections, diarrhea and infection-induced wheezing for several years after the termination of breast-feeding. Furthermore, it seems that breast-feeding decreases the risk of attracting celiac disease and allergic diseases. The latter has been much debated, but a recent critical review of published reports gives good support for long-term protection of allergic diseases, especially in high-risk children.