Final answer:
The only food an infant needs until 4-6 months of age is breast milk or formula, which provides all essential nutrients. After about 4-6 months, other foods can be gradually introduced as the infant's digestive development permits and as they become ready to explore new textures and flavors.
Step-by-step explanation:
The appropriate time to introduce foods other than breast milk or formula to infants is at 4-6 months of age. During the first few months of life, breast milk or formula provides all the necessary nutrients and hydration that an infant requires. Starting at about 4-6 months old, babies can begin to try other foods in addition to breast milk or formula, as their digestive systems begin to develop to handle more solid food. This period also aligns with the appearance of a baby's first teeth, the beginnings of motor skills that facilitate solid food intake, and a natural interest in exploring new tastes and textures.
Moreover, the composition of breast milk changes to match the nutritional needs of the baby. Colostrum is provided in the first few days postpartum, followed by transitional milk, and then mature milk, which continues to evolve during feedings. The foremilk, consumed at the beginning of a feeding, is watery to quench thirst, while the hindmilk, consumed towards the end of a feeding, is richer in fat to satisfy hunger.