Compartmental modeling of postprandial dietary nitrogen distribution in humans

A linear 11-compartment model was developed to describe and simulate the po stprandial distribution of dietary nitrogen. The values of its 15 constant diffusion coefficients were estimated from the experimental measurement of N-15 nitrogen kinetics in the intestine, blood, and urine after the oral ad ministration of N-15-labeled milk protein in humans. Model structure develo pment, parameter estimation, and sensibility analysis were achieved using S AAM II and SIMUSOLV softwares. The model was validated at each stage of its development by testing successively its a priori and a posteriori identifi ability. The model predicted that, 8 h after a meal, the dietary nitrogen r etained in the body comprised 28% free amino acids and 72% protein similar to 30% being recovered in the splanchnic bed vs. 70% in the peripheral area . Twelve hours after the meal, these values had decreased to 18 and 23% for the free amino acid fraction and splanchnic nitrogen, respectively. Such a model constitutes a useful, explanatory tool to describe the processes inv olved in the metabolic utilization of dietary proteins.