Background: Soy milk is a major soy food in China and Japan. Isoflavones in soy food are considered to protect women again breast cancer.
Materials and methods: The effects of soy milk consumption on 7,12-dimethylbenz(a) anthracene (DMBA)-induced mammary tumors in adult female rats was investigated. Sprague-Dawley rats were given 5 mg DMBA via intragastric intubation and then assigned to receive soy milk or water in addition to a normal rodent diet. Body weights, liquid and food intake, tumor number, location and development were recorded. After 20 weeks, liver, uterus and mammary tumors were removed from the sacrificed animals and examined. Plasma 17beta-estradiol concentration was also determined.
Results: After 20 weeks of DMBA administration, all of the rats that drank soy milk developed mammary tumors, while the incidence in the control group was 70% (p <0.01). Tumor multiplicity increased in the soy milk group with borderline significance (p=0.06). Total tumor weight and size in the soy milk group were 1.5-fold greater than in the control group, without a significant difference (p>0.05). Uterine weight and plasma 17beta-estradiol concentrations were similar in the two groups.
Conclusion: Our results suggest that commercial soy milk enhanced the development of DMBA-induced mammary tumors in rats. Thus, careful consideration should be given when explaining the beneficial effects of soy food.