Plolyphenols and Isoflavors - Polyphenols and Isoflavors : Prostate cancer

Polyphenols and Isoflavones

Although the rate of prostate cancer development in Asian-born men is considerably lower than that seen in American-born men, the rates tend to equalize after Asian men live in the United States for a number of years. One of the prevailing theories for this shift is the influence of diet—as men begin to consume a "Western-style" diet that is higher in fat and carbohydrates, their risk of prostate cancer begins to rise.

But researchers also offered another possible explanation for this shift. What if the Western-style diet lacks a nutrient that was present in the original diet that offered some protection against prostate cancer development?

The primary candidates in this theory are the isoflavones found in soy and the polyphenols found in green tea, two foods that are abundant in Asian-style diets but that play a far less prominent role in Western-style diets.

Polyphenols have been shown to interrupt the growth pathways of cancer cells, while other studies have shown them to inhibit angiogenesis, the process by which tumor cells form new blood vessels to accelerate their own growth. However, the quantities needed to show a benefit can often exceed normal consumption amounts. For example, one study showed a significant decrease in the number of men who developed prostate cancer after ingesting green tea extracts—but the amount given was the equivalent of over 10 cups of tea per day.

Studies of other polyphenol-rich foods, specifically red wine and pomegranate juice, have shown that the risk of prostate cancer development or progression can be lowered even after one cup, but the data on these foods are still early or remain mixed. Nevertheless, the implication that only small changes in diet can affect prostate cancer development is certainly encouraging.

As with the polyphenols, studies have shown that isoflavones from soy, specifically genistein, daidzein, and equol, interrupt cell growth pathways and angiogenesis, and therefore might slow both the development and progression of cancer cells. In addition, isoflavones have been shown to influence the production, metabolism, and excretion of testosterone and estrogens, hormones that can play important roles in the development and spread of prostate cancer.

Unfortunately, assessing the potential effects of soy-based foods on prostate cancer growth has proven challenging, partly because the amounts of isoflavones used in the different studies varied widely, and partly because the ideal group that can benefit from isoflavones remains unknown. For example, in one study, the soy isoflavone ingestion stabilized PSA levels in most men who had undergone surgery or radiotherapy, but a similar study showed no difference in PSA levels in any of the men enrolled.

New research is exploring whether the benefits of isoflavones relate more to the processing of the nutrient in the body rather than to the quantity consumed, or whether their hormone-dependent actions and their ability to affect circulating testosterone are the more important factors. A better understanding of these mechanisms will help researchers identify those more likely to benefit from soy-based foods, and will allow them to better evaluate the effects of isoflavones on prostate cancer growth and development.