Effect of heat processing and of vegetables and fruit in human diets on 1,2-dimethylhydrazine-induced colon carcinogenesis in rats.

The purpose of the present study was to investigate the modulating effect of heat processing and of vegetables and fruit in human diets on 1,2-dimethylhydrazine (DMH)-induced colon tumors. Groups of 36-45 male Wistar rats were fed for the whole experiment, starting at 4 weeks of age, one of the following diets: a semi-synthetic animal diet (A, control); diet A to which vegetables and fruit were added (B); a raw human diet (meat, bread and eggs) supplemented with semi-synthetic compounds (C); diet C with fried or baked products (D); a complete human diet consisting of heated products, and vegetables and fruit (E). The animal diets (A and B) contained 21.6% fat energy (E), 26.0% protein E, 52.4% carbohydrate E and 10.7% (w/w) fiber. The human diets (C, D and E) contained 40.6% fat E, 13.2% protein E, 46.2% carbohydrate E and 5% (w/w) fiber. Starting at 8 weeks of age and after 4 weeks of feeding the experimental diets, each rat was s.c. injected 50 mg/kg body wt, DMH for 10 weeks once weekly. At the end of the experiment, at the age of 9 months, all rats were killed and macroscopic abnormalities were collected. The colon was examined microscopically for tumors and lesions suspected of being tumors. The results revealed a lower incidence of adenomas in rats consuming the animal diet with vegetables and fruit (B) compared with the control animal diet (A). In contrast to the animal diets, vegetables and fruit added to fried or baked human diets showed no protection at all, but even increased the incidence of carcinomas. Heat processing alone had no significant effect on the DMH-induced tumor incidence. As the fat content and heat processing were main variables between the animal and human diets containing vegetables and fruit, the results obtained suggest that one of these factors or both influence the tumor-modulating effect of non-nutrient substances in vegetables and fruit.