What Every Breast Cancer Patient Must Take

Dr. Frank Shallenberger, MD

October 14, 2019



For several years now, I have specialized in treating patients with cancer. I’ve treated everything from newly diagnosed cases to advanced stage 3 and 4 cases. Many of these latter cases have failed to respond to conventional therapy.

These folks often have nowhere else to go. I’ve treated quite a few breast-cancer cases. And one of the most frequent questions I hear from these patients is, “Can I eat soy?” They have a good reason to ask this question. But my response to them might surprise you.

Soy contains phytoestrogens. A phytoestrogen is a molecule that, although it is not estrogen, is similar to the estrogen molecule. So similar, in fact, that it has an effect on the way estrogen works.

Many patients who have breast cancer or prostate cancer know that estrogen can make their cancers worse. Naturally, this causes concern about whether or not it’s safe to eat soy. To make matters worse, there are quite a few companies out there making their living off selling supplements that are soy-free. And much of what they’re putting out there has an awful lot of misinformation in it about soy.

Inevitably the anti-soy information is unfounded. They base much of the information on either misleading epidemiological studies or on studies done on infants whose diets consisted almost exclusively of 100% soy. So that’s where I come in. I actually look at the studies they refer to in detail. And I also have the experience of seeing what happens in the real world of clinical medicine. So, if you have breast or prostate cancer, or if you are at risk of getting one of these cancers, I can look you right in the face and tell you that not only is eating soy a safe thing to do, it’s also a good thing to do. That’s why I put so much in my Super Immune QuickStart.

Now a recent study on the use of soy and breast cancer is fully validating everything I have said about soy.

But before I get to the study, let me make one thing very clear.

There is soy, a food our Creator made, and then there is genetically modified soy (also known as GMO soy), which men manufactured in a laboratory. The latter is far from natural. Monsanto and DuPont originally created GMO soy. Now other chemical companies are creating new strains. I’ll explain the difference to you in a later article. For now, just remember that real soy and GMO soy are very different and have very different effects on your body. What I’m about to tell you has to do with real soy. I wouldn’t trust GMO soy in anything other than glues and car parts. So now let me tell you a few things about real soy.

The Truth About Soy

First, the phytoestrogens in soy serve as estrogen regulators. That is, in a state of estrogen deficiency they can have an estrogenic effect. But in states of estrogen excess, they can have an antiestrogen effect.

Basically, they can serve to keep your estrogen levels in a healthy balance.

Next, they have several powerful anti-cancer effects. One is the inhibition of DNA topoisomerase I and II proteases. These enzymes are critical for many breast cancers to survive.

Soy proteins also interfere with another enzyme that cancers often depend on — the tyrosine kinase enzyme. Conventional medicine has developed expensive drugs to inhibit these very same enzymes. But soy does it without any side effects.

Other studies show that soy is anti-angiogenic. That is, it acts to deprive a cancer from developing the increase in circulation it requires to grow and spread. Once again, there are very powerful drugs that have an anti-angiogenic effect. But it’s nice to know that soy does the same thing.

Soy and Breast Cancer

Now let’s get back to the study I mentioned earlier on soy and breast cancer. This study looked at the effects of eating various amounts of soy in 5,042 women. All of these women had breast cancer. The women were between the ages of 20 and 75 years old. And the study followed them for three to seven years.

What these researchers discovered was astonishing!

Across the board, the women who ate more than 9.45 grams of soy a day were 30% less likely to die during the study. In addition to this, they also were 30% less likely to have a recurrence of the cancer.

But the results were even more amazing when they compared the women with estrogen-positive cancer with those who had estrogen-negative cancers.

The results were basically the same. Even the women with estrogen negative cancers responded well to eating soy. So not only does eating soy have a very significant protective effect against breast cancer, but it also appears that this effect is not just because it modifies estrogen’s action.

It is also because of the enzyme effects I mentioned earlier. And there might be some other enzyme actions we don’t even know about yet.

Does Soy Interfere with Tamoxifen?

Another concern with women and breast cancer centers around the use of soy and the drug tamoxifen. Many doctors treat women with estrogen-positive breast cancer with tamoxifen. This drug blocks the estrogen receptors on cells, and thereby slows down and inhibits estrogen-positive cancer growth. But since soy also has estrogen-regulating effects, there has been some concern that somehow eating soy may interfere with tamoxifen.

Fortunately, one recently published paper looks at the answer to this question. The study comes out of the Department of Epidemiology at the University of California in Berkeley.

In this study, researchers followed 1,954 women for a little over six years. All of the women had conventional therapy for breast cancer. Out of this group, 282 had a recurrence of their cancer. Overall, that’s one in every six patients. (I maintain that this is way too many, but that’s another story.)

The researchers looked at all of the women in the total group who had taken tamoxifen as a breast cancer preventive. Then they analyzed the amount of soy each one had eaten during the six years of follow up.

What they found was that the women who had eaten the most soy “had an approximately 60% reduction in breast cancer recurrence” compared to those eating the lowest amounts. This is an amazing finding. And the researchers admitted it: “Soy isoflavones consumed at levels comparable to those in Asian populations may reduce the risk of cancer recurrence in women receiving tamoxifen therapy and moreover, appears not to interfere with tamoxifen efficacy.” Hopefully, that will settle the soy/tamoxifen question.

Of course, it’s better not to get breast cancer in the first place. Then you don’t have to worry about recurrence. If you’ve had breast cancer, you can help reduce your risk of breast cancer and help your children avoid this disease (that’s now a part of their family history) the same way.

An NIH study found that the amount of soy you ate as a child influences your risk of breast cancer later in life. This study involved 597 cases of breast cancer and 966 controls (Asian American) aged 20–55 years. Those in the highest third of soy intake in childhood and adolescence had a 60% reduction in breast cancer as an adult. Those in the middle third had less protection. And those in the lowest third had the least protection.

Soy can be beneficial no matter when you start it. So, please pass this information along so that others can make an informed decision about their diets. And if your children are still in your home, don’t be afraid to feed them soy foods.

Younger children may turn their noses up at tofu at first. That’s ok. Offer a variety of soy foods. Soy sprouts are terrific. But the most superior soy products are the fermented products like tofu, miso, and tempeh. If you can get your children used to these foods when they’re young, they’ll have a healthy habit that will benefit them well into adulthood. That’s some positive family history you can pass on, no matter what your genetic history includes.

The bottom line is if you have breast cancer or have had it in the past, no matter what kind it is, or if you have a strong family history, eat soy. Try to get at least 10 grams of soy in your diet every day. I put 2½ grams in every scoop of QuickStart, and you can get the rest from miso, tempeh, tofu, and even soy milk products. Just make sure that what you are eating is organic. The label will say so. Any other form of soy is genetically modified.


Guha, N., M.L. Kwan, C.P. Quesenberry Jr., E.K. Weltzien, A.L. Castillo, and B.J. Caan. “Soy isoflavones and risk of cancer recurrence in a cohort of breast cancer survivors: the Life After Cancer Epidemiology study.” Breast Cancer Res Treat. 2009 November;118(2):395-405. Epub 2009 February 17.

Shu, XO, Y. Zheng, H. Cai, K. Gu, Z. Chen, W. Zheng, and W. Lu. “Soy food intake and breast cancer survival.” JAMA. 2009 December 9;302(22):2437-43.


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