Lysine requirements of healthy adult Indian subjects receiving long-term feeding, measured with a 24-h indicator amino acid oxidation and balance technique

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Abstract
Background: The mean lysine requirement of healthy Indian subjects was estimated from short-term experimental diet periods to be 29 mg · kg−1 · d−1, which is higher than the 1985 FAO/WHO/UNU upper requirement of 12 mg · kg−1 · d−1. Objective: Our objective was to confirm our proposed requirement of 29 mg · kg−1 · d−1 by extending the diet period to 21 d and by using 4 test lysine intakes (12, 20, 28, and 36 mg · kg−1 · d−1) and a 24-h indicator amino acid oxidation and balance approach. Design: During two 21-d diet periods, 18 healthy Indian men were randomly assigned to receive 12 and 28 or 20 and 36 mg lysine · kg−1 · d−1 as part of an l-amino acid diet. At 1800 on days 6 and 20, [13C]leucine was infused over 24 h to assess leucine oxidation and daily leucine balance at each test intake. Results: Leucine oxidation, balance, and flux did not differ significantly between days 7 and 21. Twenty-four–hour leucine oxidation was lower at lysine intakes of 28 and 36 mg than at 12 and 20 mg. Leucine balances at lysine intakes of 12 and 20 mg were negative and significantly less than equilibrium (P < 0.01) and lower (P < 0.02) than balances at 28 and 36 mg lysine. Two-phase regression analysis indicated a breakpoint at 31 mg lysine · kg−1 · d−1 in the relation between lysine intake and 24-h leucine oxidation and balance. Conclusions: Full adaptation to a low lysine intake occurs within 7 d. The previously proposed tentative mean lysine requirement for Western subjects of 30 mg · kg−1 · d−1 is confirmed for healthy Indian adults.

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