Effects of wheat, rice, corn, and soybean bran on 1,2‐dimethylhydrazine‐induced large bowel tumorigenesis in F344 rats

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Abstract
This study was designed to determine the relative effects of four dietary brans on large bowel tumorigenesis in rats treated with 1,2‐dimethylhydrazine (DMH). Four‐week‐old F344 rats were fed a 20% bran (either wheat, rice, corn, or soybean) semisynthetic diet or a no‐fiber‐added control diet for life. All rats except for one control diet for life. All rats except for one control group were injected with DMH (2SC doses; ∼150 mg/kg body weight) at 8 and 10 weeks of age. Two additional groups were fed the control diet and then at 4 and 18 weeks, respectively, after the second DMH dose, were fed the wheat bran diet. All surviving rats were killed 9 months following the first DMH dose. Survival was increased in all groups receiving bran diets. Large bowel tumor incidences in the DMH group were as follows: control, 95%; wheat, 75%; rice, 86%; corn, 100%; soybean, 84%; wheat after 4 weeks, 62% (lower than control group, p < 0.05); wheat after 18 weeks, 84%. All but one of the DMH groups had approximately two tumors/tumor‐positive rat; the corn group had four. The effect of bran on large bowel carcinogenesis appears to depend both on the source of bran and when it is fed in relation to tumor initiation.