Title: Nutrient requirements of term and preterm infants Author
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: October 12, 2005
Publication Date: July 20, 2006
Citation: Heird, W.C. 2006. Nutrient requirements of term and preterm infants. In: Burg, F.D., Ingelfinger, J.R., Polin, R.A., Gershon, A.A., editors. Current Pediatric Therapy. 18th edition. Philadelphia, PA: Saunders Elsevier. p. 66-71. Technical Abstract: Growth of the healthy breast-fed term infant is the most widely accepted standard for growth from birth through 4-6 months of age. Thus, it is logical to assume that the amounts of each nutrient ingested by the breast-fed term infant during this period are adequate and the most recent dietary reference intakes for the 0- to 6-month-old term infant reflect the amount of each nutrient in the average volume of human milk ingested by 0- to 6-month-old breast-fed infants (i.e., 780 ml/d). Currently available term formulas provide even greater amounts of most nutrients. Thus, unless there is an underlying condition that limits intake, interferes with absorption or increases nutrient needs, most breast-fed infants receive adequate amounts of all nutrients for the first 4-6 months of life and formula-fed infants receive adequate intakes for even longer. There is no equally satisfactory standard for growth of preterm infants. Rather, the nutrient requirements of these infants are usually defined as the amounts of each necessary to support intrauterine rates of growth as well as nutrient accretion. Unfortunately, considering the many advantages of human milk (e.g., fewer common infections; better neurodevelopmental outcomes), the rate of growth of preterm infants fed unsupplemented human milk are lower than intrauterine rates. Further, even if the total protein, calcium, phosphorus, sodium and, perhaps, zinc contents of a reasonable volume of human milk were absorbed and completely retained, the amounts retained would not be sufficient to support intrauterine rates of accretion. If the requirements for supporting intrauterine rates of growth and nutrient deposition are provided from birth onward, the low birthweight infant (LBW) infant, in theory, should continue to grow as if birth had not intervened. However, few LBW infants make a successful transition to enteral intake until some time after birth. Most lose a minimum of 10% of initial weight during the first week of life and do not regain this until 1-3 weeks later. Some of this weight loss, probably about half, reflects loss of excess extracellular fluid and is of little consequence to the infant, but the remainder reflects primarily loss of lean body mass and may have serious consequences for the infant. Even if intakes sufficient to support intrauterine rates of nutrient accretion are provided, few infants regain birthweight before at least 2 weeks of age. Further, providing these intakes throughout the remainder of hospitalization does not prevent the infant's weighing less than a fetus of the same postconceptional age and, at discharge, approx. 90% weigh less than the tenth percentile of intrauterine standards. A likely contributor to this growth retardation at discharge is failure of the protein and energy intakes that support intrauterine rates of weight gain and protein accretion to replenish any loss of lean body mass prior to the infant's regaining birth weight. Doing so requires an additional allowance for "catch-up" growth, which varies considerably from infant to infant and is additional to the needs for supporting intrauterine rates of growth and nutrient accretion. These differing needs for "catch-up" growth make it difficult to define nutrient requirements that are appropriate for all preterm infants. Rather, each infant has a unique requirement consisting of the need for maintaining intrauterine rates of growth and nutrient retention plus the needs for "catch-up".