Effect of Soybean Trypsin Inhibitor and Isoflavone on Chemically Induced Mammary Tumor in Rats

Many researchers have reported the anti-carcinogenic effects of soybean. Isoflavone and trypsin inhibitor are identified as the effective substances. We have also shown such effects of soybean whey (rich source of trypsin inhibitor) in chemically induced skin-tumor mice and hepatoma rats. Last year we switched dietary protein from soybean to casein and were not successful to observe such effects of soybean whey and embryo bud (EB, rich source of isoflavone) on skin tumor in mice. In this study we tried to confirm such results in rats induced mammary tumor by chemical carcinogen. We fed control, whey or EB diet to female SD strain rats. Control diet contained 30% casein (isoflavone-free, trypsin inhibitor - free ), EB diet contained 27% casein plus 3%> EB (isoflavone 18.6 mg/100 g, trypsin inhibitor-free), and whey diet contained 27.5% casein plus 2.5% whey (isoflavone 0.5 mg/100 g, trypsin inhibitor 1,440 U/100 g) for 18 weeks. Rats were administered chemical carcinogen orally at the first week of the study, sacrificed at 18th week and incidence, number and weight of mammary tumor were measured. The result showed no difference in the mammary tumor among the three dietary groups, suggesting that soybean whey and isoflavone are effective to prevent cancer when soybean protein is used but not when casein is used.