Soy protein isolate and protection against cancer.
OBJECTIVE
Results from epidemiological and animal studies suggest that consuming soy-containing diets reduces the incidence of certain cancers. The purpose of this presentation was to evaluate the potential of soy protein to prevent occurrence of prostate, breast and colon cancer.


METHODS
Meta-analyses of published epidemiologic studies associating cancer risk with soy intake were performed. The incidence of chemically-induced mammary or colon tumors was determined for rats fed AIN-93G diets made with either casein or soy protein isolate (SPI). Western and Northern blot and microarray analyses were performed on rat mammary and colon tissues to study mechanisms underlying the effects of soy.


RESULTS
Meta-analyses revealed reductions in the mean overall risk estimate for mammary (0.78, p < 0.001), colon (0.70, p < 0.001) and prostate (0.66, p < 0.001) cancer for soy consumers. The incidence of AOM-induced colon tumors and DMBA-induced mammary tumors was reduced (p < 0.05) in rats fed SPI-containing diets. Lower incidence of mammary tumors in SPI-fed rats was associated with: 1) reduced terminal end bud numbers (p < 0.05), 2) lower expression of the phase I enzyme CYP1B1 (p < 0.05) and 3) reduced expression of the Ah Receptor and ARNT (p < 0.05).


CONCLUSIONS
SPI may protect against cancer via multiple mechanisms, including: 1) increased mammary gland differentiation, 2) decreased activation of procarcinogens to carcinogens and 3) regulation of genes in signal transduction pathways underlying tumor initiation, promotion and/or progression.
Badger
Thomas M
TM
Arkansas Children's Nutrition Center and Department of Physiology/Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR 72202, USA. badgerthomasm@uams.edu
Ronis
Martin J J
MJ
Simmen
Rosalia C M
RC
Simmen
Frank A
FA
D000818:Animals; D001943:Breast Neoplasms / Q000453:epidemiology / Q000517:prevention & control*; D003110:Colonic Neoplasms / Q000453:epidemiology / Q000517:prevention & control*; D004044:Dietary Proteins / Q000008:administration & dosage / Q000378:metabolism; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D046228:Microarray Analysis; D016017:Odds Ratio; D011471:Prostatic Neoplasms / Q000453:epidemiology / Q000517:prevention & control*; D051381:Rats; D017207:Rats, Sprague-Dawley; D030262:Soybean Proteins / Q000008:administration & dosage* / Q000378:metabolism
D004044:Dietary Proteins; D030262:Soybean Proteins