Of particular importance from the findings in these various metabolic studies, was the observation that the protein value of
this soy isolate when tested in children and adults was consid
erably higher than what would be predicted from the PER assay
carried out in rapidly growing rats. The latter assay seriously
underestimates the nutritional quality of the soy isolate for children and adults. Perhaps the discrepancy between ‘ ‘rat’ ‘ and ‘ ‘human’ ‘ data also explains why there appears to be a lingering
view held by some professionals as well as consumers that soy
proteins arc of poor quality. Clearly the more recent, direct hu
man metabolic data reveal that they can be and are of high nu
tritional value. Parenthetically, the question of the need for methioninc sup
plementation emerges here. From our own studies and those of
others ( 17, 18), methionine supplementation of soy proteins is
clearly unnecessary in adults. Soy proteins, consumed as isolates or concentrates, are excellent sole sources for meeting nitrogen and all amino acid needs when consumed at physiologically important intakes of total protein. Methionine supplementation of
soy-based infant formulas may, however, be desirable, although
the methioninc addition required to achieve high utilization of soy protein appears modest ( 18, 32) and is considerably lower
than would have been predicted from rat PER assay data. More than 30 y have passed since the 1957 report of the first
FAO protein requirements committee (2 1 ), who selected protein,
or amino acid, scoring as an official basis for assessing the nutritional value of proteins for meeting human nutritional require
ments. Provided that an adjustment is made for the digestibility of ingested proteins (or the availability of the indispensable
amino acids in the protein), the conclusion made by this group ‘ ‘that the concept of a desirable pattern of essential amino acid
has a great advantage and by comparison, with such a pattern, data on the amino acid content of individual foods and food com
binations can be appraised for a wide range of situations, with respect to evaluation of the nutritional quality of the diet and of
methods of improving it’ ‘ remains valid. In addition, the recent recommendations made by FAOIWHO ( 19) are entirely consis
tent with this view.
.