Availability to Man of Amino Acids from Foods

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Abstract
The replacement of a portion of the 12 amino acids in purified diets by those in wheat or in corn resulted in a slight improvement in nitrogen balance of human subjects. Since this improvement was slight and of uncertain significance, the results of the present investigation indicate that availability of an amino acid in natural food can be determined for man by feeding in alternate periods an equivalent amount of a purified and of a bound amino acid in food. Either basal diet I, containing liberal quantities of essential amino acids, or basal diet II, containing moderate quantities of essential amino acids, appears suitable for use as a control diet in studying the availability of an amino acid in food. It seems that man is able to use efficiently a combination of bound (protein-amino acids) and of purified amino acids even when all of certain amino acids, i.e., valine, leucine and phenylalanine, are ingested as bound amino acids from corn and when a major portion of certain others, i.e., lysine and tryptophan, are ingested in purified form. Differences in the composition of the basal diet in the present investigation may have affected Caloric requirement.