Absence of an inhibitory effect of a vegetables‐fruit mixture on the initiation and promotion phases of azoxymethane‐induced colorectal carcinogenesis in rats fed low‐ or high‐fat diets

Abstract

The potential inhibitory effects of a vegetables‐fruit mixture on the initiation and promotion phases of azoxymethane‐induced colorectal carcinogenesis were examined in rats fed low‐ or high‐fat diets. Rats were fed low‐fat diets (20 energy percent, Diets A and B) or high‐fat diets (40 energy percent, Diets C and D), supplemented with a vegetables‐fruit mixture (19.5% wt/wt, Diets B and D) or unsupplemented (Diets A and C) for 36 weeks. After the animals were maintained on the respective diets for four weeks, they were given three weekly injections of azoxy‐methane at 15 mg/kg body wt sc. Eight weeks after the start of the study, animals maintained on Diet A were switched to Diet B or C or maintained on the same diet. Animals maintained on Diet B or D were switched to Diet A or C, respectively. Furthermore, animals maintained on Diet C were switched to Diet A or D or maintained on the same diet. Multiplicity of colorectal tumors did not differ between groups fed a vegetables‐fruit mixture during the initiation or the promotion phase (Group B ? Avs. Group A ? B; Group D ? C vs. Group C ? D). However, multiplicity was significantly lower in animals fed low‐fat diets than in animals fed high‐fat diets in combination with a vegetables‐fruit mixture (Group A ? B/B ? A vs. Group C ? D/D ? C). Furthermore, multiplicity was significantly increased in groups fed a high‐fat diet during the promotion phase only in comparison with animals fed a low‐fat diet during the whole experiment (Group A ? C vs. Group A ? A). No other differences in multiplicity or tumor incidences were observed among the eight experimental groups.