Wheat bran (WB) increases fecal bulk and hastens colonic transit, whereas resistant starch (RS) has effects on colonic fermentation, including increasing concentrations of butyrate.We hypothesized that a diet combining WB with RS would produce more favorable changes in fecal variables (eg, fecal bulk, rapid transit time, lower pH, and higher butyrate) than would WB alone.This was a randomized crossover block-design study for which 20 volunteers with a family history of colorectal cancer were recruited. The study included 3 diets: control, WB (12 g fiber/d), and WBRS (12 g WB fiber/d plus 22 g RS/d), each continued for 3 wk. In each diet, the major source of protein was lean red meat. During 5 consecutive days (days 15-19) of each dietary period, the subjects collected their total fecal output for analysis.The WB diet resulted in greater fecal output (by 23% and 21% for wet and dry weights, respectively) and a lesser transit time (-11 h) than did the control diet but did not have major effects on fermentation variables. Compared with the control diet, the WBRS diet resulted in greater fecal output (by 56%) and a shorter transit time (-10 h), lower fecal pH (-0.15 units), higher fecal concentration (by 14%) and daily excretion (by 101%) of acetate, higher fecal concentration (by 79%) and daily excretion (by 162%) of butyrate, a higher fecal ratio of butyrate to total short-chain fatty acids (by 45%), and lower concentrations of total phenols (-34%) and ammonia (-27%).Combining WB with RS had more benefits than did WB alone. This finding may have important implications for the dietary modulation of luminal contents, especially in the distal colon (the most common site of tumor formation).