Soy isoflavones inhibits the growth of colon cancer
Epidemiological studies suggest that diets high in soy isoflavones over an entire lifetime, as seen in many Asian countries, may protect against several cancers, including colon cancer.A Canadian study lead by Jayadey Raju demonstrated that a lifetime exposure to soy isoflavones inhibited the growth of colon cancer in male Sprague-Dawley rats. This protective effect maybe linked to the increased expression of estrogen-beta receptors but the exact mechanism by which isoflavones act during colon carcinogenesis is still not established.
The rats were divided in three groups: a control group, a low-dose group (40 mg isoflavones per kg feed) or high-dose group (1000 mg isoflavones per kg feed). The rats were already exposed as embryo to soy isoflavones by feeding them to the mother rats. After birth they received soy isoflavones through mother milk and later they were fed for a period of 26 weeks, after which they were killed and analysed. The colon cancer was induced in rats by treating them with the carcinogen azoxymethane. The researchers found no influence of the soy isoflavones on the incidences or multiplicities of colon aberrant crypt foci or colon tumours, but the size of the colon tumours was decreased in low-dose group. All rats in of the control and low-dose group developed colon tumours but 5% of those in the high-dose group did not, indicating a protective effect of isoflavones. The administration of soy isoflavones showed no toxic effects or changes in behavioural, hematological or biochemical parameters.[add]The study concluded that pre- and postnatal exposure to soy isoflavones may suppress the growth of colon cancer in male rats. Other experimental studies have shown conflicting results on the link between isoflavones and colon cancer and provide only modest support for a protective effect.
Source: Raju J, Bielecki A, Caldwell D, Lok E, Taylor M, Kapal K, Curran I, Cooke GM, Bird RP, Mehta R. Soy Isoflavones Modulate Azoxymethane-Induced Rat Colon Carcinogenesis Exposed Pre- and Postnatally and Inhibit Growth of DLD-1 Human Colon Adenocarcinoma Cells by Increasing the Expression of Estrogen Receptor-beta. J Nutr. 2009 Mar;139(3):474-81.