Soy. That little three-letter word that strikes fear into the stomachs of so many. Why are we so afraid of soy? Well, I bet you’re asking…
What’s So Great About Soy?
In 2009, results from a study of over 5,000 Chinese breast cancer survivors stated that women who consumed three cups of soy milk per day were less likely to have a recurrence or to die of breast cancer than women who only drank ½ cup a day!
Soy also contains phytoestrogens (aka plant estrogens), which are pretty similar to the estrogen formed naturally in your body. Soy has a high level of phytoestrogens, but still only has a teeny-weeny bit of the power of human estrogen – just two percent! Phytoestrogens will bind to your cells’ estrogen receptors, but oddly enough, at the same time phytoestrogens can bind up estrogen to stop it from working.
And most people don’t realize that soy is not the only plant to contain phytoestrogens. Believe it or not, over 300 plants contain them, including flax, sesame, wheat, oats, barley, beans, yams, apples, carrots and pomegranates.
Can I Eat Soy If I Have Breast Cancer?
Soy can seem kinda scary if you have breast cancer that is estrogen-receptor positive (ER+). But scientists are starting to unlock this mystery of how soy works in the body with breast cancer. What they have found is that many cells in the body have estrogen receptors. Think of these receptors like little locks that need estrogen to act as the key to open them.
So estrogen unlocks these doors and lets breast cancer cells grow and multiply. But phytoestrogens fit into these same locks but cannot open the doors so they wind up competing with your natural estrogen and blocking it from working!
On top of that, phytoestrogens help to prevent cancer cells from talking to each other and ganging up on you. Phytoestrogens also stop the growth of blood vessels to tumors to cut off cancer cells’ nutrition and fiddle with processes involved in DNA that mess up how cancer cells grow and multiply. Cool!
Now, if you have what is called human epidermal growth factor receptor 2 (HER-2) positive breast cancer and are on a drug called trastuzumab (Herceptin), soy may actually help trastuzumab work better. Late breaking news: Breast cancer cells treated with genistein along with trastuzumab significantly slowed breast cancer cell growth more than using just the drug alone![i] On top of that, genistein has been shown to suppress HER-2 activity!
If you are on the drug tamoxifen, then soy may help you, too. Many people on tamoxifen are told by their docs to avoid soy because tamoxifen’s job is to block those estrogen receptors, and the thinking is that tamoxifen might bind to the phytoestrogen in soy instead.
But, back in 2007, researchers in Israel found that genistein may actually sensitize ER+ and HER-2+- breast cancer cells to tamoxifen and help it work better. Genistein and tamoxifen together caused breast cancer cells to self-destruct by targeting receptors on the cell surface and telling them to stop making something called “survivin,” which, you guessed it, helps cancer cells survive and ignore signals to self-destruct.[ii]
What If I’m A Breast Cancer Survivor?
First of all, congrats for making it through a long and difficult journey! And to reward you, you can add soy to your diet, too! In 2009, results from a study of over 5,000 Chinese breast cancer survivors stated that women who consumed three cups of soy milk per day were less likely to have a recurrence or to die of breast cancer than women who only drank ½ cup a day![iii]
And last month, researchers found that the risk of recurrence for postmenopausal breast cancer survivors was 33 percent lower for Chinese women who ate more than 42 mg/day of isoflavones – that’s only ¼ cup tofu a day! And they found this was especially true for women with ER+ breast cancer and who were taking anastrozole (Arimidex).[iv] Okay, yes, these were all Chinese women who grew up eating soy. But we could learn a lesson from them. What makes a big difference is the type of soy that’s eaten, and that we actually eat it!
What Kinds Of Soy Should I Eat?
Definitely choose organically grown soy, which by definition means that it will also be what is called “non-GMO” (non-genetically modified organism). Genetically modified (GM) soy is scary! Over 90 percent of soy grown in the United States is modified genetically to be resistant to herbicides sprayed on fields to kill off weeds. As a result, GM soy is now contained in up to 70 percent of all food products including cereals, pasta, breads and even meat since animals are fed GM soy as part of their feed to help them grow faster. GM soy has been linked to allergies, birth defects, infertility and cell mutations in the liver and pancreas. Yikes!
Also be sure to get the least processed forms of soy in your diet: edamame, soy nuts, soy milk or tofu. And by all means, experiment with fermented soy options like tempeh, miso, tamari soy sauce or natto. If you’re still scared of soy, it’s good to know that fermenting soy lowers the phytoestrogen content found in soy. Since some of the carbohydrates in soy are broken down during fermentation that means less jet propulsion from gas. Bonus!
But that doesn’t mean all you eat is soy, soy, soy each day. Make sure you get a variety of beans, legumes, nuts and grains in your diet each day to round out your protein intake. Based on the studies out there right now, you should aim to get at least one serving of soy each day – that’s ¼ cup of tofu or tempeh, one cup of soy milk or a small handful of soy nuts. Get your soy on!
[i] Lattrich C, Lubig J, Springwald A, et al. Additive effects of trastuzumab and genistein on human breast cancer cells. Anticancer Drugs. 2010 Dec 14. [Epub ahead of print]
[ii] Mai Z, Blackburn GL, Zhou JR. Genistein sensitizes inhibitory effect of tamoxifen on the growth of estrogen receptor-positive and HER2-overexpressing human breast cancer cells. Mol Carcinog. 2007;46(7):534-542.
[iii] Shu XO, Zheng Y, Cai H, et al. Soy Food Intake and Breast Cancer Survival. JAMA. 2009;302(22):2437-2443.
[iv] Kang X, Zhang Q, Wang S, et al. Effect of soy isoflavones on breast cancer recurrence and death for patients receiving adjuvant endocrine therapy. Can Med Assoc J. 2010;182(17):1857-1862.