Final answer:
Breast milk undergoes composition changes from colostrum in the early lactation days to transitional milk, and then to mature milk, which is perfectly suited to the infant’s nutritional needs. These changes, driven by hormonal regulation, are essential to support the infant's growth and mother's energy demands for milk production.
Step-by-step explanation:
It is true that breast milk differs in volume and composition over time and during a single feeding. In the first days of lactation, the mammary glands produce colostrum, a high-protein, lower-fat substance that transitions into transitional milk around the third postpartum day. Mature breast milk, which follows transitional milk around day 10, contains more lactose and balance of nutrients suited to the infant's needs. Changes in breast milk composition also occur within a single feeding: the initial milk is more watery and low in fat, while the milk towards the end of a feeding is richer in fat and calories.
The changes in composition are vital for the infant’s developmental needs. Several hormones, including prolactin, oxytocin, and insulin, regulate the composition and production of breast milk. Additionally, lactating mothers require extra food to meet the energy demands of producing breast milk, where for every 80 Kcal of milk energy produced, the mother must expend 100 Kcal.
Moreover, cow's milk is not suitable for infants due to its composition and proteins, which are difficult for an infant's digestive system to handle, reinforcing the unique adaptability of human breast milk to a growing baby's nutritional demands.