Branched-chain amino acid interactions with reference to amino acid requirements in adult men: valine metabolism at different leucine intakes

Abstract

We explored whether the oxidation of valine and by implication the physiological requirement for this amino acid are affected by changes in leucine intake over a physiological range. Six young adult men received, in random order, four L-amino acid-based diets for 5 d supplying either 20 or 10 mg valine.kg body wt-1.d-1, each in combination with 80 or 40 mg leucine.kg-1.d-1. On day 6 subjects were studied with an 8-h continuous intravenous infusion of [1-13C]valine (and [2H3]leucine) to determine valine oxidation in the fasted state (first 3 h) and fed state (last 5 h). Valine oxidation in the fasted state was similar among all diets but was lower (P less than 0.05) in the fed state for the 10 vs 20 mg valine.kg-1.d-1 intake. Leucine intake did not affect valine oxidation. Mean daily valine balance approximated +1.3 mg.kg-1.d-1 for the 20-mg intake and -1.6 mg.kg-1.d-1 for the 10-mg intake. These findings support our previously suggested mean valine requirement estimate of approximately 20 mg.kg-1.d-1.