Research Library
Effect of intact and isoflavone-depleted soy protein on NMU-induced rat mammary tumorigenesis.
Authors: Cohen LA; Zhao Z; Pittman B; Scimeca JA
Source: Carcinogenesis 2000 May;21(5):929-35
Experiments in animal models of carcinogenesis suggest that soy
consumption decreases tumor number and incidence. Genistein, an
isoflavone which is present in soy at high concentrations, has been
considered to be the primary antitumor constituent in soy. In the
present study, the N-nitroso-N-methylurea (NMU)-induced mammary tumor
model was used as a means to determine whether the chemopreventive
effect of soy was attributable specifically to its high content of
isoflavones. Five groups of rats (30/group) were fed the following
modified AIN-93G diets: group 1, 20% intact soy protein (SP); group
2, 10% SP; group 3, 20% isoflavone-depleted soy protein (IDSP); group
4, 10% IDSP; group 5, the casein-based AIN-93G diet. The SP contained
1.07 and IDSP 0.073 mg genistein/g isolate, respectively.
Experimental diets were initiated 1 week prior to NMU administration
(at 50 days of age) and continued for another 18 weeks. No
significant differences were found among the five groups when
assessed in terms of tumor incidence, latency, multiplicity or
volume. A trend towards inhibition was observed in both the 20 and
10% SP and IDSP groups when assessed in terms of total tumors/group,
tumor volume and latency, but this trend did not achieve statistical
significance. The results of this model study do not support the
hypothesis that the isoflavone components of soy protein, or soy
protein itself, inhibit chemically induced mammary tumor development.