I have written on this subject quite a few times. Here is one of my write ups:
Phytoestrogens DO NOT promote cancer. Phytoestrogens are on average 200 to 400 times weaker than the body's own estrogens. They can lock up estrogen receptors though blocking the actions of stronger estrogens. This is why many studies have found anti-cancer properties to soy and other phytoestrogen sources. In fact many phytoestrogens and phytoestrogens are routinely used to fight cancer. Red clover blossoms for example, which contains the same phytoestrogens found in soy plus two others. And resveratrol from grape skins, which is also a phytoestrogen.
And what about broccoli and other cruciferous vegetables, which are also phytoestrogen sources. And seaweeds that have a long history of being used in the treatment of cancer.
Many of the common foods we eat, and that are considered healthy, are actually phytoestrogen sources. These include sage, parsley, yams, peas, kudzu, beans, peanuts, seaweeds, carrots, bananas, oranges, millet, corn, barley, grapes, berries, baker's yeast, beets, pomegranates, cherries, garlic, oats, olives, peppers, wheat, sunflower seeds, flax seed, rye, spinach, sesame seeds, pumpkin seeds, quinoa, rhubarb, tomatoes, rice, plums, potatoes, papaya, dates, eggplant, cabbage, broccoli, cauliflower, anise, fennel, cucumber, peanuts, and onions.
And there are beverages people think are healthy, at least in moderation. These include green tea, grape juice, and wines. Beer, ouzo, gin, and whiskey are also very high in phytoestrogens.
Then there are flavonoids, which also have phytoestrogen-like effects. These are also found in many foods including berries and onions.
Bottom line is that if people really want to avoid phytoestrogens they will pretty much need to stop eating and drinking.
Luckily phytoestrogens provide numerous health benefits including protecting us from cancer and improving bone strength.
As a side note, anyone remember the "Grape Cancer Cure"? The only thing I can see in grapes that would allow them to be highly effective against cancer are the phytoestrogens in the grapes.
As for soy and its phytoestrogens, I think this myth of phytoestrogens promoting cancer just keep getting spread around by anti-soy proponents to scare people away from soy. I have seen so many myths about soy being posted on message boards and have even received them in my e-mails.