Requirements and recommended dietary intakes of protein during infancy

Two approaches have been used to arrive at estimates of the requirement for protein by infants. The factorial approach consists of adding the requirement for growth to the requirement for replacement of inevitable losses in urine and feces and from the skin. Protein requirement estimated in this way was 1.98 g.kg-1.d-1 during the 1st mo of life and decreased rapidly to 1.18 g.kg-1.d-1 by 4 to 5 mo of age, then remained at about that level to age 1 y. Believing that protein intakes of the breast-fed infant are near the level of the requirement, researchers used the intakes of breast-fed infants as a second estimate of requirement. Although intakes of protein by breast-fed infants during the first 2 mo of life are generally similar to the requirement values estimated by the factorial approach, intakes from 2 to 6 mo of age are less than the requirement values estimated by the factorial approach. Possible explanations for the discrepancy are presented. Recommended dietary intakes of protein somewhat greater than the requirements estimated by the factorial approach are proposed. These recommended intakes are less than those proposed by the FAO/WHO/UNU "safe levels of protein intake" and are less than the Recommended Dietary Allowances of the Food and Nutrition Board.