Ever since the recognition of Osborne and Mendel,1 in the early years of the present century, of the dietary indispensability of certain amino acids, physicians, nutritionists, and others have looked forward to the practical possibility of improving the protein value of certain foods by direct supplementation with specific amino acids. This hope can now be partly satisfied because of the availability of l-lysine, dl-methionine and l-cystine in commercial quantities at a reasonable price. There is no doubt that the addition of lysine to wheat products results in a significant improvement in the nutritive value of the proteins.2 Likewise, small additions of cystine or methionine improve the protein value of milk, meat, soy, and other leguminous vegetables.2 However, care must be taken not to allow initial enthusiasm to exceed proved scientific evidence.
The formation of tissue proteins is an "all or none" proposition in the
BLOCK RJ, ANDERSON DW, HOWARD HW, BAUER CD. Effect of Supplementing Soybean Proteins with Lysine and Other Amino Acids. AMA Am J Dis Child. 1956;92(2):126-130. doi:10.1001/archpedi.1956.02060030120003