Excretion and degradation of dietary fiber constituents in ileostomy subjects consuming a low fiber diet with and without brewer's spent grain

Excretion of total dietary fiber and dietary fiber components was studied in 10 human subjects with ileostomies, consuming in a crossover design a low fiber diet (15 g total dietary fiber/d) or this diet supplemented with 62 g/d of brewer's spent grain. Food and excreta were collected and analyzed on d 2, 3 and 7 of each dietary period. No significant differences in excretion of total dietary fiber or dietary fiber components were found on the three days. Excreta from subjects consuming the low fiber diet contained significantly more total dietary fiber than was ingested (20%, P < 0.01), indicating the importance of endogenous and microbial material, contributing to the total dietary fiber value, in ileostomy effluents. Analysis of specific dietary fiber components showed that this increased excretion was mainly due to fucose, mannose, galactose and uronic acid residues. When the high-fiber diet was consumed, there was a significantly greater excretion of the same non-starch polysaccharide residues as for consumption of the low fiber diet, but with a simultaneous decrease in excretion of arabinose, xylose and glucose residues (12%, P < 0.01), which were the major fiber components in the diet.