Soy and Prostate Cancer
~ November 2005 No.199 ~
Soybeans and soybean products have become very popular as people search for alternatives to animal proteins. That, and the fact that there is growing evidence that consumption of soy products may be beneficial to women’s health in particular, has resulted in a flood of soy based products in the supermarket. The health promoting properties of soy may also be of interest to men.
In a recently published article, US researchers carried out a meta-analysis on data from published scientific articles that were looking at the relationship between consumption of soybean and soybean products and prostate cancer in men. A meta-analysis is a statistical analysis that combines data from many studies that are similar in design and objectives, as a way of increasing the amount of data used to make conclusions. The power of the statistical analysis is increased and patterns and trends can become clearer.
Yan and Spitznagel were able to use data from 8 epidemiological studies that investigated the relationship between soy (tofu, soymilk, soy foods, genistein) consumption, and prostate cancer. Taken together, the studies supported the conclusion that the consumption of soy food was related to an approximately 30% reduction in prostate cancer risk in men. They quote other work that concludes that the protective effect of soy is a least 4 times greater than any other dietary factor.
As with any epidemiological survey, the question remains : “How does soy work to protect against prostate cancer?” Evidence seems to point to a family of compounds called isoflavones as the active ingredient in soy products. Eating soy products causes a build up of isoflavones in the prostate. Isoflavones appear to promote a process called apoptosis. Apoptosis is the process where cells initiate their own death. By encouraging apoptosis, soy isoflavones may be preventing cancerous cells from growing and spreading. Isoflavones may also inhibit angiogenesis, or the growth of new blood vessels, which is necessary for tumour survival. As cancers grow, they need nutrients that are carried to them via blood vessels. If new blood vessels cannot be grown as the cancer develops, the tumour growth will be slowed or stopped.
There seems to be good reason for all of us - both men and women - to include more soy products in our diets.
Meta-analysis of soy food and risk of prostate cancer in men.
Int J Cancer 2005,1117:667-669