UBC Theses and Dissertations
Nonessential amino acid metabolism in humans Cooper, Leah
Nutritionally, there is a dietary requirement for the essential amino acids (EAA) but also a requirement for nitrogen (N) intake for the de novo synthesis of the nonessential amino acids (NEAA). It has been suggested that some NEAA may be more metabolically important than others. The first study (Glutamate Requirement Study) aims to examine the application of the indicator amino acid oxidation (IAAO) technique to determine if a dietary requirement for glutamate exists in adult humans. The second study (NEAA Study) aims to determine the metabolic demand of nine of the NEAA (Ala, Arg, Asn, Asp, Gln, Glu, Gly, Pro, Ser) as an ideal N source using the IAAO technique. Seven subjects were maintained on an adaptation diet for 2 days prior to each test day. Each subject participated in two or eleven test diet intakes, assigned randomly, in the glutamate study and the NEAA study, respectively. In the glutamate study, the diets corresponded to the amino acid pattern present in egg protein, in which all glutamate and glutamine was present as glutamate, or removed, with serine used to make the diets isonitrogenous. In the NEAA Study, one test intake was a base diet consisting of only the EAA provided at the recommended dietary allowance. All other test intakes involved the base diet with the addition of one NEAA to meet a 50:50 ratio of EAA: NEAA on a N basis. Each study day followed the IAAO protocol using L-[1-¹³C]-Phenylalanine as the indicator. Breath and urine samples were collected at baseline and isotopic steady state. Enrichments of ¹³C in breath were analyzed by isotope ratio mass spectrometry to calculate F¹³CO₂. In the glutamate study, a paired-samples t-test did not find a significant difference between the F¹³CO₂ in response to the two glutamate intakes. In the NEAA study, repeated measures ANOVA with post hoc multiple comparisons showed that seven of the nine NEAA decrease IAAO significantly. Thus the results suggest that in healthy adults, there is no dietary requirement for glutamate, and that most NEAA are good N sources, in the presence of adequate EAA.
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