Apparent Small Intestinal Absorption of Nitrogen and Minerals from Soy and Meat-protein-based Diets. A Study on Human Ileostomy Subjects

The apparent absorption of nitrogen and minerals was studied in 8 ileostomy subjects. Four different test diets containing 60 g of meat, rice and bread protein, or a 25% replacement of the protein with soy flour, soy concentrate or soy isolate, were randomly assigned to the subjects in 2-d periods. All animal protein was replaced by soy isolate for a fifth 2-d period in two of the subjects. Ileostomy contents were collected in 2-h intervals during the day and in one portion during night and immediately deep-frozen. The fiber components and the phytic acid in the diet were almost completely recovered in the ileostomy contents, whereas unabsorbed starch was less than 2% of the intake. A significantly lower protein digestibility was observed when the diets containing soy protein were fed. No difference in protein digestibility was found between the different soy protein products. A 25% replacement by soy protein had no obvious effect on apparent mineral absorption. A low protein digestibility was also observed when soy was the main source of protein, and a negative apparent absorption of zinc was found in both subjects. Although 25% of soy protein in the diet does not seem to impair mineral absorption significantly, small intestinal net absorption of nitrogen is less from the soy diets than from the meat diet.