daily valine requirement of healthy adult Indians determined by the 24-h indicator amino acid balance approach

BACKGROUND: The 1985 FAO/WHO/UNU requirement for valine was set at 10 mg · kg⁻¹ · 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 · kg⁻¹ · d⁻¹) as the 1985 FAO/WHO/UNU value (14 mg · kg⁻¹ · 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 · kg⁻¹ · 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 · kg⁻¹ · 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 · kg⁻¹ · 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 · kg⁻¹ · d⁻¹ (95% Fieller's CI: 11, > 35 and 11, 28 mg · kg⁻¹ · d⁻¹, respectively). CONCLUSION: From the 24-h IAAO/IAAB approach, a mean valine requirement of 17 mg · kg⁻¹ · d⁻¹ is proposed for healthy, well-nourished Indian adults.