The daily phenylalanine requirement of healthy Indian adults.

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.