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NUTRITIONAL REQUIREMENTS
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The nutrient requirements of children are influenced by (1) growth rate, (2) body composition, and (3) composition of new growth. These factors vary with age and are especially important during early postnatal life. Growth rates are higher in early infancy than at any other period of life (Table 11–1). Growth rates normally decline rapidly starting in the third month of postnatal life (proportionately later in infants who were born preterm).
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Nutrient requirements also depend on body composition. In the adult, the brain, which accounts for only 2% of body weight, contributes 19% to the total basal energy expenditure. In contrast, in a full-term neonate, the brain accounts for 10% of body weight and for 44% of total energy needs under basal conditions. Thus, in the young infant, total basal energy expenditure and the energy requirement of the brain are relatively high.
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Composition of new tissue is a third factor influencing nutrient requirements. For example, fat should account for about 40% of weight gain between birth and 4 months but for only 3% between 24 and 36 months. The corresponding figures for protein are 11% and 21%; for water, 45% and 68%. The high rate of fat deposition in early infancy impacts not only energy requirements but also the optimal composition of infant feedings.
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Because of the high nutrient requirements for growth and the body composition, the young infant is especially vulnerable to undernutrition. Slowed physical growth is an early and prominent sign of undernutrition in the young infant. The limited fat stores of the very young infant mean that energy reserves are modest. The relatively large size and continued growth of the brain render the central nervous system (CNS) especially vulnerable to the effects of malnutrition in ...