14 DAY TRIAL // The secret of Chinese health is clearly found in the soy. Studies have shown many effects of a soy diet, including maintenance of a slim figure. But for women, the positive effects of the soy go further. A new meta-analysis carried out at the Georgetown University Medical Center and published in the "British Journal of Cancer" points that genistein, an isoflavone (estrogen mimicking chemicals) in soy, decreases the risk of developing breast cancer, especially if eaten during puberty.
"Timing seems to be vitally important in use of this bioactive food, and if we can figure out why that is so, then we may be able to help prevent breast cancer in the widest sense possible. At the present time no convincing explanation can be offered as to why the breast cancer-risk reducing effect of genistein might be strongest during childhood and early adolescence," said senior author Dr. Leena Hilakivi-Clarke, a professor of oncology at the Lombardi Comprehensive Cancer Center at Georgetown.
So far, only three human researches have connected soy consumption during puberty with later breast cancer development. Two of them were made on Asian women, whose diet traditionally includes soy. These studies found a 50% reduction in the risk of breast cancer in the case of soy consumption during childhood and adolescence.
"The strongest evidence for genistein's protective effect comes from studies in mice and rats. For example, numerous studies in rats show that the data regarding prepubertal exposure to genistein are very consistent in showing a reduction in mammary cancer risk," said Hilakivi-Clarke.
Soy exposure during fetal development or in adult life did not have a similar protective impact. The rat experiments showed that genistein consumption in puberty decreases the number of "terminal end buds" in the breast, tissue that develops the mammary epithelium (cells lining milk ducts). These epithelial cells are exactly the source of breast cancer cells.
"It is not clear if a mere reduction in the number of these structures could reduce cancer risk, or why," said Hilakivi-Clarke.
Other researches found that genistein affects the activity of genes in terminal end buds involved in cell growth, repair and death, impacting the ability of stem cells, encountered on these buds, to multiply and differentiate into specialized cells. Some researches associated an increased number of stem cells on these structures with a higher risk of breast cancer development, supporting the hypothesis that breast cancer is due to stem cells whose growth escapes control.
"Other associated research has found that the genes that genistein appears to activate in developing mammary glands are well known - BRCA1, p53, and PTEN tumor suppressors. These genes repair genetic damage and control cell survival and death, and they may also help control stem cell reproduction and genistein apparently 'up-regulates' these genes, boosting production of their beneficial proteins. What is perhaps most intriguing is that the same process that protects the breast from excess growth during pregnancy seems to be at work during puberty. In pregnancy, BRCA1 is also up-regulated, perhaps in order to control the fate of stem cells, allowing them to make more cells for milk production, for example, but not more of themselves," said Hilakivi-Clarke. It seems that genistein protects against breast cancer, just like an early first pregnancy.
"If malignancies occur in breast stem cells, then it is better that many of these cells are differentiated earlier rather than later. Pregnancy hormones do that, so the shorter time there is between puberty and pregnancy, the greater that protection may be. Genistein may also help control the fate of stem cells in the same way," said Hilakivi-Clarke.