To assess the effects of content and structure of dietary fiber (DF) on the carbohydrate digestibility and physicochemical properties of ileal digesta, five bread diets were studied in an experiment with ileum-cannulated pigs in a crossover design. The diets consisted of two experimental breads based on white wheat flour with added wheat arabinoxylan (AX) or with added isolated oat β-glucan (BG), which were compared with a low-DF commercial white wheat bread (WF) and two commercial high-DF, dark ground rye bread (GR) and rye bread with kernels (RK) as positive controls. There was no profound effect of either DF content, structure, viscosity, or water-binding capacity on the ileal digestibility of starch, which was almost completely digested in the small intestine. Arabinoxylan and β-glucan were 11 and 81% degraded in the ileum, respectively, which resulted in a significant increase and decrease of ileal extract viscosities, respectively. It is concluded that the viscosity-elevating properties of soluble DF in breads and ileal digesta are strongly dependent on the content and structure of DF and degree of resistance toward microbial enzymes.