Effect of Nonspecific Nitrogen Supplementation on Minimum Corn Protein Requirement and First-limiting Amino Acid for Adult Men

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Abstract
The minimum amount of corn protein and first-limiting amino acid in corn protein for maintenance of nitrogen equilibrium of human adults were investigated at a high constant level of total nitrogen intake. Nitrogen balances of adult men fed various proportions of corn protein nitrogen to glycine-diammonium citrate nitrogen at a total nitrogen intake of 12.45 g/day indicated a minimum corn protein requirement of between 4.0 and 5.0 g nitrogen/day under these conditions. When a slightly inadequate amount of corn protein as individually determined for each subject was fed under conditions of constant total nitrogen intake (12.45 g/day) only the inclusion of those supplements containing lysine resulted in the re-establishment of nitrogen retention. Thus, lysine is the first-limiting amino acid in corn for nitrogen equilibrium in human adults under the condition of high total nitrogen intake.
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