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Daily requirement for total sulfur amino acids of chronically undernourished Indian men^1,2,3

¹ From the Department of Physiology and Division of Nutrition (AVK and SV) and the Department of Biochemistry (JG), St John’s Medical College, Bangalore, India, and the Laboratory of Human Nutrition, Massachusetts Institute of Technology, Cambridge (MMR and VRY).

Background: Earlier studies of the requirement for total sulfur amino acids (SAAs; methionine in the absence of cystine) in healthy, well-nourished Indians indicated a value of 15 mg · kg^–1 · d^–1, but it is unknown whether this estimate is applicable to chronically undernourished subjects.

Objective: We assessed the total SAA requirement in otherwise clinically healthy, young, chronically undernourished adult Indians by using 7 test methionine intakes (3, 6, 9, 13, 18, 21, and 24 mg · kg^–1 · d^–1), without cystine, and by using both the 24-h indicator amino acid oxidation (24-h IAAO) and the 24-h indicator amino acid balance (24-h IAAB) methods.

Design: Twenty-one men were studied during each of 3 randomly assigned 7-d diet periods supplying methionine intakes (diet devoid of cystine) above and below the putative total 1985 FAO/WHO/UNU SAA requirement of 13 mg · kg^–1 · d^–1. Twenty-four–hour IAAO and IAAB were measured on day 7 by use of a 24-h [¹³C]leucine tracer infusion. The breakpoint in the relation between these values and methionine intake was determined.

Results: Two-phase linear regression of daily leucine oxidation or the daily leucine balance against methionine intake estimated a breakpoint in the response curve at a methionine intake of 16 mg · kg^–1 · d^–1 (95% Fiellers CI: 13, 22 mg · kg^–1 · d^–1).

Conclusions: On the basis of the 24-h IAAO-IAAB approach, a mean total SAA requirement of 16 mg · kg^–1 · d^–1 is proposed for undernourished Indian adults. This is not significantly different from that determined in Western and Indian well-nourished adults.

Key Words: Indian undernourished adults • methionine requirement • sulfur amino acid requirement • 24-h indicator amino acid oxidation • 24-h indicator amino acid balance

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