infant. Zimecki and coworkers (1987) reported that certain protein fractions in human milk may aid in generating helper cell responses and in performing other immunoregulatory functions. Finally, the presence of anti-idiotypic antibodies in milk may act as immunizing agents; these antibodies mimic other antibodies in the infant that in turn are directed against the original stimulating microbial antigens in the mother; thus, they may be natural, safe immunizing agents (Okamoto and Ogra, 1989).
A wealth of evidence indicates that human milk possesses many unique characteristics related to its content of nutrients, protective substances, and other components. Some evidence suggests that maternal and environmental influences are stronger than previously recognized and appreciated. If maternal intake of one or more nutrients is chronically low, certain nutrients and nonnutrient constituents of milk may decrease, with the potential for a negative impact on the nursing infant. There is mounting evidence that the concentrations of some constituents are preserved in milk at the expense of maternal reserves.
There is abundant evidence that women are able to produce milk with adequate content of protein, fat, carbohydrate, and most minerals even when their supply of nutrients is limited. The nutrients in human milk most likely to be present in lower than normal concentrations in response to chronically low maternal intakes are the vitamins, especially vitamins B6, B12, A, and D. Those maintained at the expense of maternal stores or tissues include the macronutrients, most minerals, and folate.
The kinds of fatty acids present in human milk are strongly influenced by maternal diet: the type and amount of fat in the diet and the adequacy of energy intake. However, maternal total fat and cholesterol intake have no apparent influence on the total fat and cholesterol contents of human milk.
Encourage breastfeeding mothers to consume good sources of all essential nutrients for their own health as well as to maintain adequate concentrations of nutrients in milk. Nutrients of special concern from the standpoint of milk composition are vitamin B6 and, for complete vegetarians, vitamins B12 and D.
Since many nutrients are secreted in human milk at the expense of maternal reserves, give breastfeeding women dietary guidance to maintain their own health as well as that of their infants (see Chapter 9).