Abstract
We studied the effects of amount and source of nonspecific nitrogen (NSN) on the oxidation of leucine and hydroxylation of phenylalanine. In phase 1, seven adult males received for 6 d diets providing indispensable amino acid intakes to meet the 1985 FAO/WHO/UNU (FAO) requirements or our proposed requirement values (MIT). During one diet period with each diet, the NSN of the basal diets (total nitrogen intake: 107 mg N-kg-1·d-1) was increased to a total of 160 mg N·kg-1·d-1. On the morning of day 7, an 8-h constant intravenous tracer-infusion protocol (3-h fast; 5-h fed state) was conducted with L-[1-13C]leucine, L-[ring-2H5]phenylalanine, and L-[3,3,2H2]-tyrosine as tracers. In phase 2, six subjects were given three diets for 6 d, supplying 107 mg N·kg-1·d-1; NSN was a mixture of dispensable amino acids in which glutamine accounted for 0%, 12.5%, and 100% of total NSN. Leucine oxidation and phenylalanine hydroxylation rates and whole-body leucine and phenylalanine balances were unaffected by addition of supplemental NSN to the diets in phase 1 or by amino acid source of NSN in phase 2. Leucine and phenylalanine balances were lower (P < 0.05) for FAO compared with MIT diets.
Original language | English (US) |
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Pages (from-to) | 1347-1355 |
Number of pages | 9 |
Journal | American Journal of Clinical Nutrition |
Volume | 59 |
Issue number | 6 |
State | Published - Jun 1994 |
Externally published | Yes |
Keywords
- Amino acids
- Kinetics
- Leucine
- Phenylalanine
- Requirements
ASJC Scopus subject areas
- Nutrition and Dietetics
- Medicine (miscellaneous)