The confusion surrounding soy continues. This confusion is fueled by the fact that many studies show significant benefits from soy intake while others urge caution. Some websites have declared soy a poison and others a health food. I can tell you that although some have very strong feelings for or against soy, as usual, the truth most likely lies somewhere in the middle. My opinion is that soy has some proven beneficial effects but may cause problems with over-consumption. The question I want to clear up in this writing is whether you should avoid soy due to it being an estrogen.

I recently had a patient tell me that her medical doctor told her to stay away from soy because it was an estrogen and could potentially increase her risks for, especially, breast cancer. She also didn’t want my patient to let her little girls eat soy for fear that it could cause them to reach puberty at an early age. (I will comment on this topic in the following article.) My patient then proceeded to email all of her girlfriends to warn them about the dangers of using soy. So, is soy an estrogen and should you be concerned about its use?

First, let me tell you that soy IS NOT the same as estrogen. Why people continue to say that it is, however, is actually quite understandable. The chemical structure of soy is similar to that of the estrogens. But, it is different. And, this difference is extremely important. Here is a great example of why this difference is important. Testosterone and Progesterone both have very similar chemical structures to Estrogen. However, they are completely different in how they affect your body. Thus, saying that soy is similar to the estrogens in its chemical structure means very little. Jumping from it looks like estrogen to it then must have the same effects as estrogen is not good science or good logic.

The other confusing aspect of soy is that it actually does have a low affinity for estrogen receptors in the body. In other words, soy will actually bind to or attach to estrogen receptors. You may then think that since it looks like estrogen and it binds to estrogen receptors, it must be like estrogen. And this is the assumption that confuses so many people including my patient’s medical doctor.

The best way for me to illustrate why this assumption is wrong is for you to picture in your mind a pilot sitting at the controls of an airplane. He has master control over everything in front of him and he can influence the airplane in many ways. The pilot is the “Estrogen” of the plane sitting in his proper receptor. Now picture yourself sitting in that same seat (if you actually are a pilot, think of someone else who is not). You are very similar to the real pilot in many ways even though you are different. Can you control or influence the plane in the same way as the pilot? Of course, no! Just because you can sit in the same seat (receptor) and you look similar does not mean you are a pilot (Estrogen). This analogy holds true in describing how soy and estrogen are related.

O.K., soy is obviously not the same as estrogen. There is no one who can argue against that statement. But, the isoflavones (phytoestrogens) do sit in the pilot’s seat and we do not know exactly what they are capable of doing when they sit there. Thus, it is logical to conclude that there is a chance that soy could exert some of the same functions as estrogen. It is also logical to then ask the question of whether there is a danger of developing cancer from soy intake. The only place we can turn is to the scientific literature for answers. Below are just a few of the recent studies showing benefits of soy intake towards the development or treatment of different types of cancer.

Breast Cancer

Study: Soy phytochemicals synergistically enhance the preventive effect of Tamoxifen on the growth of estrogen-dependent human breast carcinoma in mice. Harvard Medical School

Conclusion: The combination of Tamoxifen with genistein (phytoestrogen from soy) had synergistic effects on DELAYING the growth of MCF-7 tumors. (They slowed breast cancer cell growth.)

Study: Genistein (phytoestrogen from soy) protects human mammary epithelial cells from benzo(a)pyrene-7,8-dihydrodiol-9, 10-epoxide and 4-hydroxy-2-nonenal genotoxicity by modulating the glutathione/glutathione S-transferase system.

Conclusion: Epidemiological studies have shown that ingestion of isoflavone-rich soy products is associated with a reduced risk for the development of breast cancer. Genistein pretreatment PROTECTS normal breast cells from certain carcinogens (cancer causing chemicals), suggesting that dietary-mediated induction of detoxification may be a mechanism contributing to prevention against gene injury in the development of breast cancer.

Study: Soyfood intake in the prevention of breast cancer risk in women: a meta-analysis of observational epidemiological studies.

Conclusion: This meta-analysis supported the hypotheses that soyfood intake may be associated with a DECREASED risk of breast cancer due to the isoflavones.

Ovarian Cancer

Study: Genistein-induced apoptosis and autophagocytosis in ovarian cancer cells. Gynecol Oncol 2007 Apr:105(1):23-30

Conclusion: Genistein is CYTOTOXIC (kills cells) to ovarian cancer cells.

Kidney Cancer

Study: Progression of renal cell carcinoma is inhibited by genistein and radiation in an orthotopic model. BMC Cancer. 2007 Jan 9;7:4.

Conclusion: Genistein SLOWS the progression of kidney cancer.

Colorectal Cancer

Study: Dietary phytoestrogen intake is associated with reduced colorectal cancer risk. J Nutr. 2006 Dec;136(12):3046-53.

Conclusion: Genistein intake is associated with a REDUCED RISK of colorectal cancer.

Prostate Cancer

Study: Genistein inhibits the contact-stimulated migration of prostate cancer cells.

Conclusion: The results of several epidemiological studies have suggested that a soybean-based diet is associated with a lower risk of prostate cancer. These results show that at physiological concentrations, genistein exerts an INHIBITORY effect on the migration of prostate cancer cells and suggest that it may be one of the factors responsible for the anti-metastatic activity of plant isoflavonoids.

I find it puzzling how my patient’s doctor could so confidently have come to the conclusion that soy intake was associated with cancer development. I know two things for sure:

1. Human and animal studies show an overwhelming benefit of soy towards cancer.

2. Soy is not the same as estrogen.

The conclusion I come to is that soy, taken in moderate amounts, is not bad. Drinking small amounts of soy milk or eating soy products every now and then is not going to cause you harm unless you have a sensitivity to soy. I do think that there are problems with, especially, genetically modified soy and that is why I do not simply suggest eating soy in large amounts without any concern.

I encourage anyone who disagrees with me to email me and I will publish your points in future issues of Health Zingers.