Nutrition and Metabolism of Proteins 67above the mean or average requirement. It is not
surprising, therefore, that the UN and IDECG require-
ments disagreed. This also shows why recommenda-
tions by different national and international expert
groups differ; they interpret the same data differently,
use different data, and also may choose to set differ-
ent criteria for judging the adequacy of intake.
Further, as is characteristic of various estimates of
human nutrient requirements in general, it must be
appreciated that the values given in Table 4.9 are
based on limited data; the values for the preschool
children are derived from a single set of investigations
carried out at the Institute for Central America and
Panama, while those for the school-aged children
come from studies conducted by a single group of
investigators in Japan. Those for adults are based pri-
marily on the nitrogen balance studies in men carried
out in the 1950s and 1960s. There are multiple reasons
for questioning the precise reliability and nutritional
signifi cance of the adult values, and they include the
facts that adult amino acid requirement values (Table
4.9) are greatly infl uenced by:
● the inappropriate experimental design used earlier
for estimation of requirements
● the inadequacy of the nitrogen balance technique
and the criterion of nitrogen balance that has been
used to judge the nutritional adequacy of the levels
of amino acid intake tested.
Therefore, some contemporary and newly pro-
posed amino acid requirement estimates for adults
are shown in Table 4.10. The more recent values are
generally very different from the recommendations
made in 1985. It is important to remain alert in nutri-
tion, as these texts will emphasize. At the time of
writing the original text, a new UN expert group was
meeting to consider all of the new data that had been
accumulated in the past 20 years. It was expected that
new recommendations would be made in 2002 or
2003, but, since they have not been published, the
recommendations by the Institute of Medicine of the
US Academies of Science have been added as a sepa-
rate column in Table 4.10. The important point,
however, is that all is not set in stone. Nutritional
knowledge continues to advance, and with it the rec-
ommendations must change or at least be responsive
to this new information.4.7 Meeting protein and amino
acid needsKnowledge of the requirements for the specifi c indis-
pensable amino acids and for total protein provides
the basis for evaluating the relative capacity (or
quality) of individual protein foods or mixtures of
food protein sources to meet human amino acid
requirements.
The two major determinants of the nutritional
quality of food proteins are:
● the content of indispensable amino acids in the
proteinTable 4.9 1985 FAO/WHO/UNUa estimates of amino acid requirements at different ages (mg/kg/day). Reproduced with permission from WHO
Amino acid Infants (3–4 months) Preschool children (2 years) School boys (10–12 years) Adults
Histidine 28?? [8–12]
Isoleucine 70 31 28 10
Leucine 161 73 44 14
Lysine 103 64 44 12
Methionine and cystine 58 28 22 13
Phenylalanine and tyrosine 125 69 22 14
Threonine 87 37 28 7
Tryptophan 17 12.5 3.3 3.5
Valine 93 38 25 10
Total 714 352 216 84
Total per g proteinb 434 320 222 111
a FAO/WHO/UNU. Technical Report Series No. 724. Geneva: World Health Organization, 1985. Data taken from Table 4, p. 65, and Table 38,
p. 121, and based on all amino acids minus histidine.
b Total mg per g crude protein.