By Christine Horner M.D.
Soy has been a food staple in the Asian diet for thousands of years. Asia has far lower rates of cancer than the United States does, and researchers think that eating a lot of soy may be one of the reasons. Japanese men and women eat about ten times more soy than American men and women. According to many studies, if you eat an adequate amount of soy often enough, your risk of breast cancer will drop by 30 to 50 percent. For instance, a study published in the Journal of the National Cancer Institute in June 2003 found the more soy women consumed, the lower was their risk. In this study women who ate two bowls of miso soup a day had a 26 percent lower risk of breast cancer. Those who ate three bowls of miso soup (a soup made with soybean paste) a day cut their risk by 40 percent!
But some physicians warn their patients not to eat soy foods because they fear that soy may increase the risk of breast cancer instead of decreasing it. How could this be? There are published studies that call into question the benefits of soy. The fear of soy raising the risk of breast cancer came initially from a study from the University of California, San Francisco, published in October 1996. In this study, women were given 38 grams of genistein (an active substance in soy—see below) a day for one year. It’s important to note that these women were not given genistein as it occurs naturally in whole soy foods. Rather, they were given genistein that had been extracted and isolated from soy foods and prepared as a supplement—a supplement composed only of genistein with none of the hundreds of other nutrients in soy. The researchers were surprised to discover that instead of having a protective effect, the genistein supplement appeared to be harmful. After one year on the genistein supplement, the women had elevated the amounts of estradiol in their blood and their breast cells showed signs of stimulation and increased growth. This unexpected result concerned researchers. Could soy actually increase the risk of cancer? Yet hundreds of other studies show that women who eat the most soy have the lowest risk of breast cancer. So, how could a genistein isolate have the opposite effect?
Here is one explanation. The women in the controversial study didn’t eat fresh whole soy foods. They were given an isolate of genistein—something that doesn’t naturally occur in Nature. When you isolate a substance from the whole, it often behaves differently. Your body was designed to eat, digest, and metabolize fresh whole foods, which contain hundreds, even thousands, of substances all interacting with one another. Those interactions can be critically important. One substance may balance the effect of another, make it more or less effective, take away its toxic effects, increase its absorption, or modify how your body uses it in some important way. Research shows that when genistein is consumed as part of whole soy foods, it’s absorbed very differently from how it is in an isolated supplemental form. Genistein in whole soy is activated by intestinal bacteria during digestion, whereas genistein taken as an isolated supplement is absorbed before it reaches the bacteria in the intestines. This may be part of the reason that genistein supplements appear to have an effect different from that of whole soy foods. So, until research shows otherwise, stay away from genistein supplements and eat whole soy foods.
GENISTEIN
There are several substances in soy that are active against breast cancer. A particular type of phytochemical, called genistein, appears to be one of the most important. Genistein is classified as a phytoestrogen, or plant estrogen, because it has a weak estrogenic effect. Two other major phytoestrogens in soy are daidzein and glycitein. However, genistein is the most abundant and well-researched of the three and is usually the only one that is listed on the label of soy products.
Research shows that genistein is extraordinarily effective at reducing the risk of breast cancer. It has been shown to stop tumor growth, prevent metastasis, and shut off new blood vessels in growing tumors. According to a 2006 study published in Medical Hypothesis, genistein attaches to a “beta” type of estrogen receptor (ERbeta), which has an antiproliferative effect as opposed to the “alpha” type of estrogen receptor that stimulates cells to grow and divide. It also blocks the cancer-promoting estrogens from attaching to the alpha estrogen receptors on breast cells.
Breast cancer is a hormonal disease. That means that a hormone causes the cancer to develop by inciting cells to grow and divide. For breast cancer, that hormone is estrogen. The more estrogen you are exposed to, the higher your risk of breast cancer is. Estrogens come in different strengths and behave differently. Strong estrogens increase your risk of cancer because they tell cells to grow and divide rapidly. Phytoestrogens and other weak estrogens decrease your risk of cancer because they slow down cell division. Genistein acts like a weak estrogen in the body. It blocks the effects of strong estrogens and slows down cell division. Genistein is very weak—in fact, less than 1/100 of the strength of estradiol (the most potent type of natural estrogen). So, if genistein attaches to an estrogen receptor, the rate of cell division is only 1/100 of the speed that it is if estradiol attaches to the receptor. The more genistein there is to compete with estradiol, the slower the rate of cell division and the lower your risk of breast cancer.
This is an extremely simplistic look at a very complicated process. Remember, soy is composed of hundreds of components all interacting together. Genistein doesn’t act alone. If it’s extracted from whole soy foods and then isolated and consumed without the other soy ingredients, it can actually have detrimental effects.
SOY CONSUMPTION IN PREPUBESCENT GIRLS
Many studies show that young girls who eat soy products before they go through puberty have a substantially lower risk of breast cancer later in life. One explanation for this finding is that a woman’s breast tissue is considered “immature” before she has had her first baby. Immature breast tissue is more sensitive to environmental toxins and other carcinogens. Soy has been found to help mature the breast tissue, making it more resistant to environmental toxins. According to a study published in Carcinogenesis in 2004, exposure to soy prior to puberty triggers another protective action—it “up-regulates” the breast cancer 1 (BRCA1) gene, a tumor-suppression gene. In other words, soy turns on a gene that suppresses tumor growth—and keeps it on. A 2012 study found that consuming soy before puberty may also contribute to lowering the risk of breast cancer by delaying puberty.
SOY AND BREAST CANCER SURVIVORS
Breast cancer survivors benefit from eating soy as well. Many studies conclude that women who eat higher levels of soy have improved survival and lower recurrence rates. A meta-analysis of eighteen studies published in 2011 by Chinese researchers suggested that the protective effects of soy at reducing the incidence and recurrences of breast cancer were significant for Asian populations and not Western populations. However, an in-depth analysis of combined cohort studies of U.S. and Chinese women published by Vanderbilt University researchers the following year found that soy benefited both populations. In this large study, women who had been diagnosed with breast cancer and who consumed more than 10 milligrams (mg) of soy isoflavones per day had a decreased risk of recurrence and mortality—regardless of where they lived.
SOME SOYS ARE BETTER THAN OTHERS
There are dozens of different types of soy foods available, but when it comes to nutrients and health-promoting qualities, not all soy products are the same. Some soy foods are far better for you than others. Most important, be sure to consume only organic soy as most soy crops in the US are genetically modified with potential health damaging effects.
Edamame
Steamed or boiled soybeans in the pod, also called edamame. Only the beans are eaten; the tough, fibrous pod is discarded.
Roasted Soybeans
Dry roasted soybeans. These make a great snack food. There are several different flavors to choose from, including ranch and, my personal favorite, Cajun.
Tempeh
This traditional Asian and Indonesian food is growing in popularity, so you can find it in most grocery stores. It’s a cultured soy cake that sometimes has other grains or spices added to it. You can cook tempeh a number of ways: Sauté it in olive oil, bake it, crumble it into salads or stews, use it as a sandwich filling, or add it to a stir-fry dish.
Tofu
Made from soymilk curd, tofu looks a little like cheese. Its own flavor is very mild, but it will pick up the flavor of any dish you add it to. You can use it in at least 101 different ways, so I suggest you get a good tofu cookbook and experiment.
Natto
This form of soy is made from fermented cooked whole soybeans. It comes in a variety of flavors and is commonly used in sushi rolls and with rice in Japanese restaurants. It’s less popular than other soy products, so you are more likely to find it in an Asian market than at your local grocery store.
Miso
Miso (fermented soybean paste) is a salty condiment that can be used to flavor a variety of dishes. Added to boiling water, it makes an excellent soup.
How much soy should you consume each day to lower your risk of breast cancer? Experts say about 4–12 ounces of a quality soy product. However, if you want to eat a little less soy than that but still get the same (or even better) cancer-fighting effects, you can add certain traditional Asian spices to your soy dishes.
About the Author
Christine Horner, M.D.
Christine Horner, M.D. is a board certified and nationally recognized surgeon, author, expert in natural medicine, professional speaker and a relentless champion for women’s health. She is the author of Waking the Warrior Goddess: Dr. Christine Horner’s Program to Protect Against and Fight Breast Cancer, winner of the Independent Book Publishers Award 2006 for Best Book in Health, Medicine, and Nutrition. www.drchristinehorner.com.