A carcinogenesis bioassay of guar gum, a widely used food stabilizer, was conducted by feeding diets containing 25,000 or 50,000 ppm of the test substance from two batches having purities of 83.5% and 91.9% to 50 F344 rats and 50 B6C3F1 mice of either sex for 103 weeks. Groups of 50 untreated rats and mice of either sex served as controls. The rodents might have tolerated higher doses but 50,000 ppm (5% of diet) is the upper limit for chronic feeding studies in the Bioassay Program, and this level represented the maximum tolerated dose (MTD) for females of both species in the present study.
After week 20 in mice and week 40 in rats, mean body weights of high-dose females were lower than those of the untreated controls. No compound-related clinical signs or adverse effects on survival were observed. Feed consumption by dosed rats and dosed mice of either sex was lower than that of the controls. There were increased incidences of adenomas of the pituitary (8/45, 18% controls; 17/46, 37% low dose; 17/43, 40% high dose) in male rats and pheochromocytomas of the adrenal (0/50, 0%; 5/50, 10%; 6/50, 12%) in female rats, but these differences (P<0.035) were considered to be unrelated to administration of guar gum. When pituitary adenomas or carcinomas and when pheochromocytomas or malignant pheochromocytomas are combined, the statistical differences disappear.
Hepatocellular carcinomas (15/44, 34%; 6/50, 12%; 6/49, 12%) occurred in treated male mice at incidences significantly (P<0.011) lower than that in controls. The combined incidence of male mice with either hepatocellular adenomas or carcinomas (16/44, 36%; 12/50, 24%; 7/49, 14%) was also significantly (P=0.013) lower in the high-dose group.
Under the conditions of this bioassay, guar gum was not carcinogenic for F344 rats or B6C3F1 mice of either sex.