ABSTRACT
BACKGROUND: The daily requirement for phenylalanine is not known with certainty. Earlier 24-h tracer studies have suggested that the requirement is between 30 and 40 mg . kg(-1) . d(-1). OBJECTIVE: The objective was to assess the phenylalanine requirement in healthy well-nourished Indians with the use of 8 test phenylalanine intakes (19, 23, 27, 31, 35, 38, 43, and 47 mg . kg(-1) . d(-1)) and the 24-h indicator amino acid oxidation (24-h IAAO) and 24-h indicator amino acid balance (24-h IAAB) methods. DESIGN: Thirty-two healthy, well-nourished Indian men were studied during each of 2 randomly assigned 6-d diet periods in which phenylalanine intakes of 19, 23, 27, 31, 35, 38, 43, and 47 mg . kg(-1) . d(-1) were supplied; the diet was devoid of tyrosine. A 24-h [13C]leucine tracer infusion was used to measure 24-h IAAO and 24-h IAAB on day 7. The breakpoint in the relation between these values and the phenylalanine intake was determined. RESULTS: Two-phase linear regression of daily leucine oxidation and balance against phenylalanine intake estimated a breakpoint in the response curve at phenylalanine intakes of 37 and 38 mg . kg(-1) . d(-1) (95% CI for both: 31, >47 mg . kg(-1) . d(-1)), respectively. CONCLUSION: On the basis of the 24-h IAAO and 24-h IAAB methods, a mean phenylalanine requirement of 38 mg . kg(-1) . d(-1) is proposed for healthy well-nourished Indian adults in the absence of tyrosine intake. This finding is similar to that in Western adults.
Subject(s)
Phenylalanine/metabolism , Adult , Amino Acids/administration & dosage , Anthropometry , Diet , Humans , India , Linear Models , Male , Nutritional Requirements , Oxidation-Reduction , Phenylalanine/administration & dosageABSTRACT
BACKGROUND: The 1985 FAO/WHO/UNU requirement for valine was set at 10 mg x kg(-1) x d(-1) on the basis of nitrogen balance studies carried out in Western subjects. It is likely that the requirement is higher, however, because the requirement of another branched-chain amino acid, leucine, was found to be about 3 times as high (40 mg x kg(-1) x d(-1)) as the 1985 FAO/WHO/UNU value (14 mg x kg(-1) x d(-1)). OBJECTIVE: We assessed the valine requirement in healthy, well-nourished Indians by using 7 test valine intakes (5, 10, 15, 20, 25, 30, and 35 mg x kg(-1) x d(-1)) and the 24-h indicator amino acid oxidation (24-h IAAO) and balance (24-h IAAB) method, with phenylalanine as the indicator amino acid, while maintaining leucine intake at 40 mg x kg(-1) x d(-1). DESIGN: Eighteen healthy, well-nourished Indian men were studied during each of 3 randomly assigned 7-d diet periods supplying valine intakes that were equally placed on either side of a putative mean valine requirement of 20 mg x kg(-1) x d(-1). Twenty-four-hour IAAO and 24-h IAAB were measured on day 7 by use of a 24-h [13C]phenylalanine tracer infusion. The breakpoint in the relation between these values and the valine intake was determined. RESULTS: Two-phase linear regression of daily phenylalanine oxidation or balance against valine intake estimated a breakpoint in the response curve at a valine intake of 17 mg x kg(-1) x d(-1) (95% Fieller's CI: 11, > 35 and 11, 28 mg x kg(-1) x d(-1), respectively). CONCLUSION: From the 24-h IAAO/IAAB approach, a mean valine requirement of 17 mg x kg(-1) x d(-1) is proposed for healthy, well-nourished Indian adults.
