SOY feeding induces phase II enzymes in rat tissues

Induction of phase II detoxification enzymes has been shown to protect against the development of cancer. Soybeans contain compounds thai are known inducers of phase II enzyme activity. In this study, male Sprague Dawley rats were fed soy flour (SF) or soy protein isolate (SPI) to provide physiological concentrations of soy ( 15 % of total protein). Rats were fed ad libitum for one and two week diet periods and compared to casein control groups (AlN-93). Hepatic glutathione S-transferase (GST) was significantly increased to 135% of control values in rats fed SF for both 1 and 2 weeks and in rats fed SPI for 2 weeks (P<0.05). Quinone reductase was significantly increased (12-14 fold) in the colon of rats fed both SF and SPI for 2 weeks (P<0.001 ) and in serum (1.8-2 fold) of the SF group at both 1 and 2 weeks. Liver UDP-glucuronosyl transferase (UDPGT) activity was significantly increased (3-5 fold) in the SPI and SF groups at 2 weeks (P<0.01). Kidney UDPGT activity was increased (3-4 fold) in the SPI group at both 1 and 2 weeks (P<0.05) and in the SF group at 2 weeks (P<0.01). UDPGT activity in the small intestine was induced 8-10 fold in both the SPI and SF groups at 1 and 2 weeks (P<0.001). There was no significant change in total liver glutathione in either diet group. The data indicates that dietary soy enhances phase II enzyme activity, especially quinone reductase and UDPGT, thus leading to protection of the organism from activated exogenous and endogenous xenobiotics that may lead to the development of cancer.