Postprandial metabolic utilization of wheat protein in humans

Abstract

Background: The quality of cereal protein has been little studied in humans despite its quantitative importance in the diet, particularly in developing countries. Objective: The objective of this study was to determine the nutritional value of wheat protein in humans as assessed by the measurement of their real ileal digestibility and postprandial retention. Design: Healthy young adults (n = 14) were fitted with an intestinal tube to allow the collection of intestinal fluid in the duodenum or terminal ileum. Subjects received a mixed meal of 136 g wheat toast that contained 24.6 g uniformly and intrinsically [15N]-labeled wheat protein. Intestinal fluid, blood, and urine were collected for 8 h postprandially. Results: The real ileal digestibility of dietary wheat nitrogen amounted to 90.3 ± 4.3%. The cumulative amount of dietary nitrogen transferred to the deamination pools reached a plateau at 8 h of 24.7 ± 6.8% of the amount ingested. The urinary excretion of dietary nitrogen in ammonia was high (0.8 ± 0.3% of ingested dose). The incorporation of dietary nitrogen into serum protein reached 7.0 ± 1.9% of the meal. Postprandial wheat protein retention was 66.1 ± 5.8%. Conclusions: Our results show that wheat proteins had the same true ileal digestibility as did most of the plant proteins already studied in humans, but also that they had a lower postprandial nitrogen retention value. However, this low value was higher than that predicted from the calculation of indispensable amino acid scores, ie, 89% rather than 30-40% of the nutritional value of milk proteins. © 2005 American Society for Clinical Nutrition.