Complementary food is needed when breast milk (or infant formula) alone is no longer sufficient for both nutritional and developmental reasons. The timing of its introduction, therefore, is an individual decision, although 6 months of exclusive breastfeeding can be recommended for most healthy term infants. The new foods are intended to ‘complement’ ongoing breastfeeding with those dietary items whose intake has become marginal or insufficient. Both breastfeeding and complementary feeding can have direct or later con- sequences on health. The evaluation of consequences of both early and late introduction of complementary food can neither disregard the effect of breastfeeding compared to formula feeding nor the composition or quality of the complementary food. Possible short-term health effects concern growth velocity and infections, and possible long-term effects may relate to atopic diseases, type 1 and 2 diabetes, obesity and neuromuscular development. On the basis of the currently available evidence, it is impossible to exactly determine the age when risks related to the start of complementary feeding are lowest or highest for most of these effects, with the possible exception of infections and early growth velocity. The present knowledge on undesirable health effects, however, is mainly based on observational studies, and although some mechanisms have been proposed, further prospective studies have to clarify these unsolved issues. Even less evidence on the consequences of the timing of complementary food introduction is available for formula-fed infants.
Breast milk is the natural nutrition for infants, but in the second half of the first year of life, complementary feeding is needed. Many complementary foods contain gluten, but gluten exposure is associated with the risk of developing celiac disease (CD). CD is a disease with considerable morbidity and mortality. Although CD is associated with certain genetic features, carrying the human leukocyte antigen haplotypes DQ2 or DQ8 (a prerequisite for CD development) cannot fully explain who will or who will not develop CD. Potential risk factors for CD include perinatal events and infant feeding practice. With the exception that children who are breastfed at and beyond gluten introduction into the diet probably may be at a lower risk of developing CD, and that heavy gluten load early in life may increase the risk of future CD, data on the impact of infant feeding are inconsistent.
The addition of solid foods to an infant’s diet is required to provide adequate nutrition, as eventually an infant will be unable to consume a sufficient volume of breast milk to meet their nutritional needs. The timing of this important dietary change for infants born preterm ( ! 37 weeks of gestation) should take into consideration their delayed early gross motor developmental progress, increased nutritional requirements, organ immaturity, increased gut permeability and increased risk of hospitalization from infections. Good head control is important for safe eating of solid foods: this developmental milestone may be delayed in preterm infants up to 3 months of corrected age. One randomized controlled trial has demonstrated improved nutritional intakes with the introduction of nutrient-dense solid foods from 13 weeks of uncorrected age, resulting in improved nutritional iron status and greater rate of growth during infancy. There is neither current evidence for an increased infection rate with an early introduction of solid foods in developed countries, nor is there evidence that in preterm infants maturation of renal function is reduced. However, one observational study has determined that preterm infants who had 4 or more solid foods introduced prior to 17 weeks of corrected age, or who had any solid foods introduced prior to 10 weeks of corrected age, had an increased risk of eczema development. A compromise is needed to balance the nutritional benefits of commencing solid foods from 13 weeks of uncorrected age with the risks of increased eczema development, along with ensuring developmental readiness. Based on the current evidence, 3 months (13 weeks) of corrected age seems to be an appropriate age to commence nutrient-dense solid foods for most preterm infants. Further research, with an emphasis on immediate as well as longer-term consequences, would be valuable to provide more specific evidence-based guidelines regarding the introduction of solid food for preterm infants.
Increased fruit and vegetable consumption early in life may lead to life-long intake of fruits and vegetables, which in turn may be beneficial for weight control and other health outcomes in later life. Although health officials worldwide recommend delaying solid foods until 6 months of age, younger infants often receive solid food, which may affect later obesity rates. The timing of introduction to solid foods is important both nutritionally and developmentally and may affect acceptance of foods both in infancy and later in life. Infants can clearly discriminate the flavors of different fruits and vegetables. Repeated flavor experiences promote the willingness to eat a variety of foods: infants will consume more of foods that have a familiar flavor and are more accepting of novel flavors if they have experience with flavour variety. Many flavors that the mother either ingests or inhales are transmitted to her milk and/or amniotic fluid. Moth- ers can help the transition from a diet exclusively of milk or
formula to a mixed diet by providing the infant familiar flavors in both milk or formula and solid foods. Exposure to a variety of flavors during and between meals appears to facilitate acceptance of novel foods. Providing novelty in the context of a familiar food might prove to be an optimal combination to progressively accustom infants to a diversity of novel foods. When repeatedly exposing infants to flavors of some vegetables that have bitter tastes, mothers should focus not on infants’ facial expressions but on their willingness to eat the food and should continue to provide repeated opportunities to taste the food. Introducing children repeatedly to individual as well as a variety of fruits and vegetables, both within and between meals, might help them be more accepting of fruits and vegetables, which is difficult to enhance beyond toddlerhood.