Babies don’t get all of their nutrients through breast milk alone. Parents are advised to supplement their breastfed babies with 400 IU of vitamin D each day starting from the first few days of life. Breastfed babies of vegan or vitamin B₁₂-deficient mothers may also require vitamin B₁₂ supplements. All newborns are also typically given an injection of vitamin K in the hospital after birth. Babies have very little vitamin K, an important blood-clotting vitamin, in their bodies because it crosses the placenta to the developing baby poorly. In addition, though it has recently been recognized that the unborn infant’s gut may contain low levels of certain bacteria that synthesize vitamin K, very little of the vitamin is absorbed from the colon where these bacteria reside.

Infants vary considerably in terms of their growth, development, nutritional needs, and feeding patterns. During the first two to six weeks of their lives, they primarily feed, sleep, and grow. By late infancy, newborn reflexes have gone away and a baby has mastered certain physical tasks that allow him to progress from a diet of exclusive breast milk or formula to foods with an increasingly wide variety of flavors and textures. The ways parents feed their babies not only nourish them, but also help to promote motor development and establish key feeding skills, healthy habits, and strong family relationships.

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Babies grow at different rates because of differing genetic factors and prenatal history, but growth is also an important indicator of adequate nutrition. Inadequate intake of calories or essential nutrients can significantly affect mental and physical development, particularly during the critical periods from birth to one year. Infants should double their birth weight by four to six months and typically triple it by their first birthday. They also grow in length by approximately 50% in their first year. (INFOGRAPHIC 17.10)

Babies who are fed on demand typically consume enough and grow appropriately, and they can eat quite a lot—about five times more in relation to their body weight than adults eat. Parents should not limit the fat intake of their children in the first two years of their life, because fat is essential for meeting caloric needs, facilitating brain development, and helping the baby’s body absorb fat-soluble vitamins.

Solid foods—which the American Academy of Pediatrics advises should be introduced around the age of six months and the World Health Organization advises should be introduced between the ages of four and six months—are intended to complement, but not replace, breast milk or formula. Infants who are exclusively breastfed for around six months have consistently been shown to have a reduced risk of gastrointestinal tract infections and grow and develop as well as infants who have solid foods introduced before six months.

According to the American Academy of Pediatrics, a baby may be ready to eat solid foods when she is able to hold up her head and sit in a high chair or feeding seat with good head control. The tongue thrusting reflex that allows a baby to suck efficiently should be diminished enough so that the infant can move food from the spoon to the back of his mouth for swallowing. Typically infants double their birth weight at around four months and weigh 13 pounds or more and may, at that point, be big enough to try solid foods. Finally, babies may indicate a readiness for solid foods when they show an interest in what the family is eating, and can signify when they are satiated, for instance by turning their head when they are full or by refusing to open their mouth. Babies who are fed solid foods before they are ready may be at risk for becoming overweight, developing food allergies, and suffering upset stomachs. (See Chapter 18 for information about food allergies). (INFOGRAPHIC 17.11)

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Following a healthy pregnancy, most—but not all—infants have iron stores to help meet their needs around four months of age, after which the risk for iron deficiency increases. Iron is necessary for the formation of brain cells, so iron deficiency can hinder psycho-motor development. Research suggests that treating young children once they have iron defi-ciencies is not enough—it does not prevent cognitive problems—so it may be more important to prevent iron deficiency from developing in the first place. Babies at the highest risk for iron deficiency are those who were born prematurely, who are fed formula that is not fortified with iron, and who are exclusively breastfed without iron supplements. Because of the risks, doctors recommend that parents begin feeding their infants iron supplements after the age of four months if babies are not being fed iron-fortified complementary foods, such as rice cereal.