Though many similarities exist, human and cow’s milk are not one and the same in gross composition or nutrient content. Cow’s milk does not fulfill an infant’s nutritional needs. This is the reason why infant formula, even one based on cow’s milk components, is a quite different food from the milk from which it is prepared. Infant formula has been changing in composition, even in recent times. United States surveys show dramatic differences in the nutrient intake of infants in the years 1977-1978, compared with 1965. Most of these differences reflect changes in infant formula, which is now manufactured to be more similar to mother’s milk, especially in gross composition (see Table 1). Keep in mind that values given in the table are averages. Differences among individuals of either groups can be very great. Cow’s milk shown in Table 1 is milk as produced in the United States. It is richer in fat content than most commercial whole milk, which, by federal regulation, need not contain more than 3.25% fat. In either case, human milk averages somewhat higher. Cow’s milk is appreciably higher in protein and mineral matter. It is primarily these latter two components that must be modified in cow’s milk if it is to be used as a substitute for mother’s milk.
More commonly referred to as milk sugar, lactose is the major carbohydrate of the milk of mammals. Human milk contains nearly 7% lactose (about 38% of caloric content), exceeding cow’s milk by about 2% and averaging nearly the highest level of any mammalian species. implies a greater need for milk sugar for human offspring than for other mammals. Energy needs per unit of body weight are indeed the highest during infancy than at any other time. Carbohydrates, a ready source of energy, are obviously important in infant nutrition. Lactose is a two-unit molecule (disaccharide) consisting of glucose and galactose. The latter component may serve a unique purpose. Along with certain lipids (fat and fatlike compounds), galactose forms a large part of brain matter. This being the case, lactose could well be present at high levels in human milk to aid in growth and development of the brain. Certainly there could be no better reason for ensuring that the infant receives ample amounts. Lactose intolerance (the inability to digest lactose readily) is another matter to be discussed later (see Chapter 9). For now it need only be said that human milk substitutes can be formulated as readily with 7% as 5% (or less) milk sugar. Lactose of cow’s milk (or of other mammals) is identical to lactose of human milk. Between mammals, only amounts differ. Healthy, full-term infants have no trouble digesting lactose. Preterm or low-weight (under 2500 g) infants may have some difficulty in this respect. For this reason, formula prepared for preterm, underweight infants is specially designed with one-third to one-half less lactose than might normally be used. The difference is made up with simple sugars (such as the glucose of corn syrup solids). The presence of an enzyme called lactase facilitates lactose digestion.