Soy-based products consumed in Asian countries are minimally processed whereas in the USA many of the soy foods and soy ingredients are highly processed. Soy foods contain
complex mixtures of bioactive compounds, which may interact with one another. The objective of this study was to evaluate the ability of various soy products containing
genistin, the
glycoside form of
genistein, to affect growth of MCF-7 cells transplanted into ovariectomized athymic mice. Products investigated included soy flour, two
crude extracts of soy (soy molasses and Novasoy(R)), a mixture of
isoflavones and
genistin in pure form. Each of the soy flour-processed products was added to the diet to provide equivalent amounts of
genistein aglycone equivalents (750 p.p.m.).
Tumors in the negative control animals regressed throughout the study while the
tumors in the soy flour-fed animals remained basically the same size (neither grew nor regressed). In animals consuming soy molasses, Novasoy(R), mixed
isoflavones or
genistin alone,
tumor growth was stimulated when compared with animals consuming a control diet devoid of soy. These same dietary treatments resulted in increased cellular proliferation. Changes in
mRNA expression of gene targets (
estrogen responsiveness, cell cycle progression, apoptosis and
aromatase activity) in
tumors induced by the different diets were evaluated. The relative expression of pS2,
progesterone receptor and
cyclin D1 was increased in animals consuming the Novasoy(R), mixed
isoflavones and
genistin. Bcl2
mRNA expression was low in most of the dietary treatment groups compared with positive (
estradiol implant) controls.
Aromatase expression was not affected in any of the treatment groups. The degree of soy flour processing affects the estrogenicity of products containing a constant amount of
genistein. Collectively, these findings suggest that for postmenopausal women with
estrogen-dependent
breast cancer, the consumption of foods containing soy flour is more advisable than consuming
isoflavones in more purified forms.