on the physiological requirements for the indispensable amino
acids and total nitrogen and on the concentration of specific
amino acids in the source of interest.
This raises the question of the content and balance of indis
pensable amino acids in plant and animal protein foods. There
are extensive data on the amino acid composition of foods (12, 13). For present summary purposes, Table 5 gives the amounts in different food sources of those indispensable amino acids that
are likely to be the most limiting in plant protein foods. As
shown, the indispensable amino acid lysine is consistently at a much lower concentration in all major plant-food protein groups
than in animal foods. In addition, the sulfur-containing amino
acids are distinctly lower in legumes and fruits and threonine is
lower in cereals compared with amounts found in proteins of
animal origin. A more extensive survey of the limiting amino
acid and the amino acid score for various plant protein foods is
presented in Table 6.
.