The amino acid requirements of man. XVI. The role of the nitrogen intake.

The preceding papers of this series have dealt with the classification of the amino acids as essential or non-essential components of the food of man (l-5), the r61e of the caloric intake when amino acids serve as virtually the sole sources of nitrogen (6)) and the quantitative amino acid needs of human subjects as measured by the maintenance of nitrogen equilibrium (7-15). One additional topic remains to be considered, namely the approximate amount of nitrogen which is required by the organism when safe intakes of the eight essentials are being consumed. Inasmuch as all of the studies previously described (1-15) have involved the use of diets containing a limited number of amino acids, care has been exercised constantly to insure the presence in the food of sufficient nitrogen to permit the synthesis by the organism of the missing amino acids. In the earlier experiments, this was accomplished by supplying rather liberal amounts of the essentials. Later, as the minimal human requirements were revealed, the quantities of the essentials were decreased, and, in their place, glycine and urea were incorporated in the food. Both of the latter compounds can be utilized by the growing rat for the purpose in question (16). No reason exists for doubting that in man they are capable of performing a like function. The present paper, which is the last of the series, is concerned with the quantity of this extra nitrogen which is necessary for the synthesis of the non-essential amino acids under the conditions specified above.