Nutritional value of [N-15]-soy protein isolate assessed from ileal digestibility and postprandial protein utilization in humans

The purpose of this work was to assess the true oro-ileal digestibility, an d to concurrently quantify the deamination of absorbed dietary nitrogen to examine the postprandial nutritional value of a soy protein isolate (SPI) i n humans. To assess bioavailability and bioutilization of SPI, 10 healthy v olunteers ingested 30 g of SPI, intrinsically and uniformly [N-15]-labeled, added with 100 g of sucrose and water up to a final Volume of 500 mL. True ileal digestibility was assessed by the [N-15]-dilution method for 8 h by means of a naso-intestinal intubation technique. To describe and quantify e xogenous nitrogen deamination for the same time period, urine and plasma sa mples were collected. True oro-ileal digestibility of SPI nitrogen was 91%. The amount of absorbed SPI amino acids used for nonoxidative disposal, i.e ., postprandial biological value, was 86% 8 h after meal ingestion. Hence, net postprandial protein utilization of SPI was 78%. Compared to previous d ata that were assessed under the same condition in humans, the nutritional value of SPI is 92% of that in milk protein concentrate.