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The daily phenylalanine requirement of healthy Indian adults ^1,3,4

¹ From the Institute of Population Health and Clinical Research, St John's National Academy of Health Sciences, Bangalore, India (AVK, TDSR, VNR, and JG), and the Laboratory of Human Nutrition, Massachusetts Institute of Technology, Cambridge, MA (MMR and VRY)

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.

Key Words: Well-nourished Indian adults • phenylalanine requirement • aromatic amino acid requirement • 24-h indicator amino acid oxidation • 24-h indicator amino acid balance

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