Once babies are born, of course, they still need adequate energy and nutrients. One of the best ways to provide this essential nutrition is through breastfeeding (lactation), which has become more common in recent years. Seventy-seven percent of U.S. newborns are breastfed by their mothers, and nearly 50% are breastfed until six months of age—up from just 35% in 2000. The American Academy of Pediatrics recommends that women exclusively breastfeed their babies through the age of six months, at which point they should continue breastfeeding—ideally to the one-year mark or beyond—while also introducing complementary solid foods.

The human breast is a gland made up of connective and fatty tissues that support and protect the milk-producing areas of the breast and give it shape. Shortly after birth, milk is produced in clusters of small sacs called alveoli. The alveoli group together and form lobules. Milk produced in the lobules travels through ducts, which eventually exit the skin in the nipple. The dark area of skin surrounding the nipple is called the areola. (INFOGRAPHIC 17.7)

The human breast does not store a large amount of milk. In fact, most milk is produced during nursing, based on need. In other words, the volume of milk produced varies with demand—the volume can go down if the mother does not nurse or pump, and the volume may increase if the baby feeds a lot. When the infant sucks on the nipple, the hormones prolactin and oxytocin are released. Prolactin stimulates milk production while oxytocin stimulates contraction (or the “let-down reflex”), which shortens and widens the milk ducts ejecting milk through the duct system and out of the nipples.

The composition of breast milk varies depending on the stage of lactation, milk volume, feeding frequency, and differences between women. However, once lactation is established, the primary components are water (87%), carbohydrates, fats, proteins, vitamins, and minerals. At the beginning of the feeding, the milk contains lactose and proteins, but little fat; it is called foremilk. The end of the feeding produces hindmilk. The hindmilk contains more fat, the main source of energy for the infant. Both are nutritious, but hindmilk has more calories and babies will be more satiated if they get both foremilk and hindmilk during feedings.

Breast milk is the ideal infant food. It provides babies with many crucial nutrients, as well as antibodies that enhance their ability to fight infections and strengthen their immune systems. Breast milk is rich in vitamins, full of essential fatty acids for brain development, contains the appropriate balance of proteins and minerals to enhance digestion, and promotes infant oral motor development. Additionally, breastfeeding also reduces the risk of diarrhea and vomiting in infants and mitigates their risk of becoming obese later in life. There is also limited evidence that it may reduce the risk for chronic diseases, such as type 2 diabetes and heart disease, later in life.

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There are also documented benefits to breastfeeding, including reductions in incidence of upper respiratory infections in the first two years of life, childhood leukemia, sudden infant death syndrome, and orthodontic problems. Evidence also exists to support higher IQ scores among children who were breastfed for at least six months. Plus, breastfeeding is convenient and less expensive than formula feeding and it plays an essential role in promoting mother–infant bonding. There are added benefits for mothers who nurse that include a reduced risk of ovarian and breast cancer, less risk of type 2 diabetes, and possibly a faster return to prepregnancy body weight. (INFOGRAPHIC 17.8)

Question 17.3