Studies of the relationship between dietary fat intake and colon-cancer risk are generally inconsistent. Animal studies show that caloric (energy) restriction will inhibit the growth of spontaneous or experimentally induced tumors. Exercise reduces the incidence of chemically induced tumors in rats and vigorous occupational activity has been shown to reduce colon-cancer risk in men. Reduced energy intake and/or increased energy output may provide a simple means for lowering cancer risk in man.