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Biological Value of Proteins in Relation to the Essential Amino Acids Which They Contain

V. Comparison of the Average Effect of Ten Single Amino Acids with Extra Egg Protein as Supplements to an Egg Diet¹

Department of Vital Economics, University of Rochester, Rochester, N. Y.

A comparison was made of the average effect on nitrogen balance of feeding to each of ten members of a diet squad a single but different one of the ten essential amino acids, with the effect of a small amount of whole egg protein added as a supplement to the same diet containing already an inadequate amount of this protein. The average total nitrogen from the amino acids fed singly as supplements should equal the nitrogen of the egg supplement. Actually owing to some vicissitudes experienced in taking some of the amino acids and the exigencies of time this ideal was not realized very exactly. Two experiments on the amino acids with different persons taking each one gave good agreement and furnished what may be called a vertical average in comparison with a horizontal (simultaneous) one on the egg supplement.

Another objective was to learn something of the relative retention potency of the several essentials and whether the total nitrogen of the racemic forms should be reckoned against the egg nitrogen or only that of the natural isomers.

The results were: (1) That the supplement of egg (learned from analyses obtained later) supplied 0.7 gm essential amino acid nitrogen of natural form, while the ten synthetic essentials supplied on the average only 0.46 gm from natural isomers. (2) That the average retention of the egg nitrogen was 0.819 gm or 71% of the total nitrogen fed, indicating that some non essential nitrogen must have been retained; while the average retention from the ten essentials was, in two experiments, 0.419 and 0.426 gm or 54.5 and 55.4%, respectively, of the average total nitrogen fed in the essentials, indicating a large wastage of nitrogen from the amino acids. (3) Calculated on the basis of the nitrogen from the natural isomers only the retentions in the two experiments were 91 and 93%, respectively. (4) The effects on biological value relative to the egg basal diet were about the same from the two types of supplement; namely a reduction of seven points in the percentage scale.

Other observations were that women appear to be better conservators of nitrogen than men, and that in fifteen of twenty tests the presence of amino acids in the diet reduced the fecal nitrogen, notwithstanding that each subject ingested from 0.43 to 1.0 gm more nitrogen than from the basal egg diet alone.

Conclusions reached were: (1) That a vertical average can be duplicated satisfactorily and furnishes much useful information, but would be still more useful after a correct analysis of the protein was in hand. (2) That the individual essential amino acids differ greatly in retention potency under the conditions of these experiments; and (3) that it is the nitrogen of the natural isomers which must be counted on to equal the effects on nitrogen balance of natural proteins.

Manuscript received 21 August 1946.