The mechanism(s) by which dietary fiber exerts beneficial effects on the growth of weanling rats fed toxic doses of amaranth (Food Red No.2, AM) was investigated. Dietary fiber was prepared from "gobo", the roots of edible burdock (Arctium lappa L.) and this preparation was called GDF. Three kinds of diets were used : a purified, low-fiber diet (basal diet), the basal diet plus 4 or 5% AM (control diet) and the control diet plus 5% GDF (test diet). (a) Growth rate, food consumption and food efficiency in rats fed the control diet were significantly lower than those in rats fed the basal diet. The values of these parameters in rats fed the test diet were almost the same as those in rats fed the basal diet. (b) When AM was added to the basal diet, water consumption (expressed as ml/g of diet consumed) was significantly increased and it moderately decreased by the concurrent feeding of GDF. (c) Stomach emptying was significantly promoted by the addition of AM to the basal diet and it was moderately retarded by the concurrent feeding of GDF, as judged by the amount of nitrogen remaining in the stomach 3 hr after feeding. (d) Dietary AM significantly lowered cecal pH, markedly increased cecal volume and produced severe diarrhea throughout the experimental period. The concurrent feeding of GDF prevented the decrease in cecal pH, expansion of cecal volume and diarrhea.(e) The liver tissues of rats fed diets containing amaranth had higher sodium levels (about twice) than rats fed the basal diet, whether or not the diet contained GDF. (f) A structural degeneration in the mucosal epithelium of the stomach, duodenum or colon was not observed in scanning electron microscopic examinations, and the gastrointestinal morphology was essentially identical in the three groups. These results suggest that the growth retardation in rats fed excessive doses of AM was partly due to inhibition of the digestive-absorptive processes without structural degeneration of the luminal mucosa and partly due to chronically depressed food consumption. The role of GDF in protection against AM toxicity is probably by controlling the transit-time of the chyme.
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