The potential of an insoluble dietary fiber‐rich source from barley to protect from DMH‐induced intestinal tumors in rats

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Abstract
The influence of soluble and insoluble dietary fiber supplements from barley and wheat on colon cancer risk was assessed using male Sprague‐Dawley rats from four weeks of age on a semipurified (AIN76A) rat diet modified to contain 20% fat of mixed animal and plant origin and 5% dietary fiber. Gastrointestinal tumors were induced with dimethylhydrazine given weekly for five weeks at 15 mg/kg body wt by subcutaneous injection, commencing four weeks after rats were established on the experimental diets. At 32 weeks of age, rats were killed and tumors assessed. The insoluble dietary fiber‐rich source from barley (spent barley grain, SBG) was significantly more effective at preventing induced tumors than soluble fiber‐rich commercial barley bran. There were no significant differences among the results for the other three fiber sources, which were intermediate in their influence. Both incidence of rats affected and tumor mass index were reduced, the latter significantly, when SBG was compared with commercial barley bran. SBG also produced a significant reduction in plasma cholesterol concentration (down 17%, p < 0.05) relative to wheat bran, but commercial barley bran was not different from wheat bran at this stage. Pure cellulose and outer‐layer barley bran were, by comparison, only moderately effective in cancer prevention. SBG, like wheat bran, is a good source of cellulose and hemicellulose. It is also a good source of proteins, polyphenolics, fatty acids (including α‐linolenic), vitamin E, and minerals. Further research is needed to clarify the relevance of these other factors to the differences observed. SBG as a dietary fiber source appears to be very effective in protecting rats from dimethylhydyazine‐induced intestinal cancer.