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J Nutr. 1999 Nov;129(11):1992-7.

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

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Institut National de la Recherche Agronomique, Unité de Nutrition Humaine et de Physiologie Intestinale, Institut National Agronomique Paris-Grignon, 75231 Paris Cédex 05, France.


The purpose of this work was to assess the true oro-ileal digestibility, and to concurrently quantify the deamination of absorbed dietary nitrogen to examine the postprandial nutritional value of a soy protein isolate (SPI) in humans. To assess bioavailability and bioutilization of SPI, 10 healthy volunteers ingested 30 g of SPI, intrinsically and uniformly [15N]-labeled, added with 100 g of sucrose and water up to a final volume of 500 mL. True ileal digestibility was assessed by the [15N]-dilution method for 8 h by means of a naso-intestinal intubation technique. To describe and quantify exogenous nitrogen deamination for the same time period, urine and plasma samples 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 data that were assessed under the same condition in humans, the nutritional value of SPI is 92% of that in milk protein concentrate.

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