Protein requirements of infants: a reexamination of concepts and approaches.

Estimates of protein requirements of infants aged 3-4 mo by FAO/WHO/UNU (1.47 +/- 0.26 g.kg-1.d-1 as crude protein, N X 6.25) are judged to be overestimates. From simulation analyses we suggest that 1.1 +/- 0.1 - 0.2 g.kg-1.d-1 is a more reasonable estimate. This is consistent with statements that 1) breast milk that provides an average of 16 g protein/1000 kcal or a fixed-composition formula that contains 17 g protein/1000 kcal is adequate for essentially all such infants and 2) average protein intakes from that milk or formula would be approximately 1.65 or 1.75 g.kg-1.d-1, close to current average requirements estimates. It appears that there has been a difference in the concepts of requirement usually applied to infants and to adults and a systematic misinterpretation of breast-milk data in estimating requirements. A plea is issued for the application of epidemiologic approaches as a part of requirement estimation.