Influence of dietary fibers on fermentation in the human large intestine

Fiber sources were fed to 24 men to evaluate the effect of fiber on large intestinal microflora. The diets were low fiber basal or the basal diet supplemented with coarse bran, fine bran, cabbage, or cellulose (Solka floc). Twelve subjects (Group 1) were fed all fiber sources using a latin square design with 2-week experimental periods followed by a 3-week period on the basal diet. Group 2 made one diet change after the first experimental period, then remained on that diet throughout the experiment; during the last period their fiber intake was double (to approximately 26 g/day). A microbial culture system was utilized with fecal microflora to measure cell wall indigestibility and volatile fatty acid (VFA) production. Volatile fatty acids were also measured in fresh feces. The in vitro substrates were alfalfa, coarse bran, cabbage, or cellulose. In this system, dietary fiber had a significant (P less than .05) effect on resultant cell wall indigestibility and VFA level. Previous diet in group 1 subjects significantly (P less than .05) affected in vitro VFA. In groups 2 significant (P less than .05) period and subject effect were present for the in vitro VFA data. The VFA concentrations in feces of humans were significantly affected by the fiber consumed.