Diets high in fat and low in dietary fiber have been associated with a higher incidence of colon cancer, possibly by increasing bile acid concentration in the colon. Therefore changes in bile acid metabolism due to beef tallow, corn bran (CB), and soy polysaccharide (SP) feeding were studied. Rats were fed one of four diets for six weeks: 5% beef tallow fiber-free (LF), 20% beef tallow fiber-free (HF), 20% beef tallow with CB (HFCB), and 20% beef tallow with SP (HFSP). HF increased fecal output compared with LF, and HFCB and HFSP increased fecal output compared with HF. HF reduced fecal bile acid concentration by two-thirds compared with LF, although daily bile acid excretion was similar. There was a tendency toward a smaller bile acid quantity in the small intestine with HF than with LF. Neither fiber altered total fecal bile acid concentration or small intestinal bile acid quantity compared with HF. However, 7 alpha-dehydroxylase activity in the colon was lower with HFSP than with HFCB. Increasing dietary beef tallow from 5% to 20% in animals fed a fiber-free diet greatly reduced the concentration of bile acids in the large intestine and feces, an effect associated with a reduced risk of colon cancer.