Some 30 randomly selected men, aged 50-59 years, were investigated in each of 4 areas--Copenhagen, Them (rural Denmark), Helsinki, and Parikkala (rural Finland)--to determine the relationship of diet, gut transit time, fecal bulk, fecal bacteriology, bile acid concentration, and urinary volatile phenol production to large bowel cancer risk. Average daily fat intake was found to be high in all 4 areas, and no differences emerged between areas. Saturated fatty acid consumption was higher in low-incidence areas than in high-incidence areas. Intakes of nonstarch polysaccharides (the main component of dietary fiber), carbohydrate, and protein (mainly milk) were higher in the low-incidence area of Parikkala than in the high-incidence area of Copenhagen. The fecal bile acid concentration was higher in the high-incidence area than in the low-incidence area, with the other 2 areas having intermediate values. Fecal bulk showed an inverse association with colorectal cancer incidence. No differences were observed with regard to fecal bacteriology or mutagenic activity of the foods. These results indicate that a population can have a low risk of colorectal cancer despite a high intake of dietary fat, protein, and meat. Dietary carbohydrate and fiber may be considered protective. One mechanism limiting colorectal cancer risk could be the increase in fecal bulk resulting from such intakes, since increased fecal bulk dilutes the increased colonic bile acid concentrations of subjects on high-fat diets.