Soy and breast cancer

Vegetarian Journal, March-April, 2005 by Reed Mangels

Breast density, as measured by mammography, is a predictor of breast cancer risk. Women with high breast densities are reported to be four to six times more likely to develop breast cancer. Many factors influence

breast density, including genetics, medications, and diet. Some studies have found that soy intake was associated with greater breast density, but results have been inconclusive. A recent large study had 109 women eat two servings of soy, providing 50 milligrams of isoflavones, every day for two years. These women were compared to a control group of 111 women who were instructed not to increase their soy intake, which was very low. After two years, there was no significant difference in breast density between the two groups. This suggests that soy consumption in adulthood does not increase breast density. This study did find that Caucasian women who reported eating more soy during their lives had a higher breast density, while women who ate soy at least weekly after they were 20 years old (but ate little soy before that) had a greater reduction in breast density during this study. Further study is needed to evaluate the role of soy intake during childhood and adolescence on breast cancer risk. The results of this study, however, suggest that moderate soy consumption by adult women has little effect on breast density and does not appear to increase risk of breast cancer.

Maskarinec G, Takata Y, Franke AA, et al. 2004. A 2-year soy intervention in premenopausal women does not change mammographic densities. J Nutr 134:3089-94.

Neuhouser ML. 2004. Soy mammographic breast density: plausible hypothesis but limited evidence in humans. J Nutr 134:2911-12.