Fecal output, gastrointestinal transit time, frequency of evacuation and apparent excretion rate of dietary fiber in young men given diets containing different levels of dietary fiber.

Five healthy young male subjects were given meals containing different levels of dietary fiber (DF) for one week each, and the effects on the fecal output, gastrointestinal transit time, frequency of evacuation, and apparent excretion rate of dietary fiber in feces were studied. The experiments were conducted twice by varying the subjects and the DF levels. The following results were obtained. 1) With an increase in the intake of DF, feces increased significantly in both wet weight and volume. The fecal specific gravity did not show any clear-cut relation with the intake level of DF. 2) The gastrointestinal transit time tended to shorten in each DF period compared to the DF-free period. However, it did not shorten with an increase in the intake level of DF. 3) Frequency of evacuation tended to be high in any of the DF periods compared to the DF-free period. However, the differences in the intake level of DF produced no changes in the frequency. 4) The DF content in feces increased significantly with an increase in the intake of DF, indicating that the larger the fecal output, the larger the fecal DF content. The apparent mean excretion rate of DF in feces remained in the range of 60-75% throughout the two experimental phases. Residues in feces other than DF increased with an increase in the DF intake. 5) The results obtained here indicate that the DF intake of at least 20 g per day produces 140-150 g of fecal output which can be easily excreted daily by a normal adult person.