Whole body branched-chain L-amino acid oxidation in overnight fasted human subjects

Catabolism of the natural branched-chain L-amino acids in overnight fasted healthy volunteers was comparatively studied by performing oral loading tests with 1-C-13-labelled L-leucine, L-valine, and L-isoleucine (38 mu mol x kg (body weight)(-1)), respectively. On the basis of the (CO2)-C-13 exhalation and the C-13-isotope enrichment in the plasma branched-chain compounds, whole body branched-chain L-amino acid oxidation rates were estimated applying a seven compartment model and non-linear regression analysis. Mean computed in vivo oxidation rates were in the order L-leucine >> L-valine > L-isoleucine and amounted to 0.32 +/- 0.06, 0.22 +/- 0.04, and 0.17 +/- 0.05 mu mol x (kg body wt.)(-1) x min(-1) (n = 5), respectively. The data are discussed with respect to current estimates of human branched-chain L-amino acid requirements.