Effect of fiber on protein, fat and calcium digestibilities and fecal cholesterol excretion.

Five female subjects were given four types of test diets containing various levels of protein for four consecutive 5-day periods and their dietary fiber and feces were collected throughout the experimental period. Diet A was a high-fiber, low-protein diet containing brown rice. Diet B was a semi-purified, low-protein diet containing agar agar as the sole source of dietary fiber. Diet C was a low-fiber, normal-protein diet containing polished rice. Diet D was a high-fiber, normal-protein diet containing brown rice. A fecal marker was given at breakfast on the first day of each five-day test period and on the day after the end of the experiment. Fecal weight increased during the period on high-fiber diets (diets A and D). The apparent digestibilities of protein and fat were significantly depressed by high-fiber diet. Fecal excretion of calcium did not increase on the high-fiber diets. A decrease in the apparent digestibility on a high-fiber, low-protein diet was partly due to the low intake of calcium during this period. Fecal excretion of cholesterol increased markedly during the periods on high-fiber diets. The difference between the intake and fecal excretion of dietary fiber suggested that the fiber was partially digested in the colon.