Modulation of the postprandial utilization of dietary protein by both qualitative and quantitative factors of the protein intake in humans

Abstract

The consequences of an increased habitual protein intake on the metabolic utilization of dietary proteins remain unclear, due to both the complexity of postprandial dynamic phenomena and the difficulty to access experimentally to the major N pools in humans. Clinical experiment was coupled with compartmental modeling for studying the combined effects of the prevailing protein level in the diet and the protein source in the meal on the postprandial metabolic fate of meal N (Nm). Healthy subjects were adapted for 7d to a normal (NP: 1 g.kg−1.d−1), and for the next 7d to a high (HP: 2 g.kg−1.d−1) protein diet. After each period, they ingested a mixed meal containing 15N-labeled milk (M), soy (S) or wheat (W) proteins and Nm kinetics were measured for 8h in some accessible pools of the ileum, blood and urine. These data were then analyzed using a 12-compartment model for assessing the postprandial kinetics of Nm in the major splanchnic and peripheral N pools. Main results: metabolic fate of Nm in % of dose at 8h Increasing the habitual protein intake led to (i) higher postprandial Nm losses by deamination and lower entero-hepatic recycling of Nm-derived urea, and (ii) a 10-25% lower peripheral anabolic utilization of dietary N. The gap between the nutritional values of M, S and W proteins was also increased at high levels of protein intake.