Cancer and Soy

From the book The Okinawa Program by Bradley J. Willcox, MD, Craig Willcox, PhD, and Makoto Suzuki, MD (Three rivers Press, NY, 2001), based on the landmark 25-year study: (Bryanna Clark Grogan’s notes in brackets[] and in bold type. The text in the book is footnoted and there is a chart of phytoestrogen content of many foods. This article was contributed by Bryanna.)

“Okinawan women get natural estrogens (natural SERMs [“selective estrogen receptor modulators”] through their diet [rather than drugs that are given to women with risk of breast cancer in our society-BCG], mainly from the large quantities of soy they consume. Soy contains phytoestrogens, or plant estrogens, called flavinoids. The other important major phytoestrogens are lignans, which are derived from flax and other grains. All plants, especially legumes (beans, peas), onions, and broccoli, contain these natural SERMs, but not nearly in the same quantity as soy and flax. Soy and flax are the undisputed king and queen of natural SERMs. The good thing about flavinoids and lignans is that they offer you protection from the damaging effects of estrogen while allowing you all the beneficial effects. Here’s how it works:

All estrogens, whether they are produced in your body or by plant, have one thing in common: they must connect with a cell receptor to work, to promote cell growth. If the estrogen receptor is blocked, the estrogen can’t connect. You can think of it as the estrogen trying to get through the cell door with a key. The receptor is the keyhole. When the keyhole is blocked by SERMs the estrogen can’t get in, and therefore can’t promote growth. That’s part of what flavinoids and lignans do: they’re estrogen blockers-but they are selective blockers; remember, SERM means selective estrogen receptor modulator. That’s the beauty of these phytoestrogens. They allow estrogen to connect and promote growth at certain selected areas of the body where it is beneficial-that is, the bones-and block it from promoting growth in sensitive sites, such as the endometrium and breasts, where it can do damage. With no extra cell growth there is much less risk of cancer.

This is important information for women in North America, where even the definition of high risk for breast cancer is scary. A high-risk woman is someone over the age of twenty-five who has at least a 1.7 percent projected risk of breast cancer in the subsequent five years-about double the average risk. This includes most women with a first-degree relative (sister, mother or daughter) who had breast cancer and all women over sixty years of age-about 29 million American women, or roughly 20 percent of all women in the United States.” (There is a lot more information that is important and I highly recommend this book to everyone.) Here’s one more quote: “Your risk as a North American woman is approximately one in ten of getting breast cancer in your lifetime.” AND “In contrast, if you are on Okinawan woman [on the traditional diet-not the modern, North American-influenced one-BCG], the chances are that no one you know has it or will develop it. You may have heard of it but have never seen it-it is that rare. There is no need for screening mammography. You have to put 100,000 Okinawan women in a room to find six who will die from it. This improves an Okinawan’s odds of living life without fear of breast cancer by more than 80 percent versus a North American woman. Even if you get breast cancer in Okinawa, your chances of dying of it are less than half as much as among North Americans.” (They go on to say that “bad genes” appear to account for only a small number of breast cancer cases. Many studies have shown that Asian women increase their risk of breast cancer when they move to North America and adopt our eating habits.)

“We belive this is the best for our health. We really like it as we drink nothing but soymilk. And it’s saving us a kaboodle of money.”

J. & M. Cherry, Mundare, AB August 2004


Only a small number of cancers can be attributed to heredity, and, when Asians immigrate to Western countries, within a couple of generations their descendants catch right up to other Westerners in terms of cancer deaths. Even in Asia itself, as the diet has become more Westernized, there has been a slow but steady rise in mortality from all types of cancer.

Studies of Japanese men on traditional high-fiber, high-vegetable, low-fat diets showed consistently that, though Japanese men get prostate cancer at the same rate as North American men, far fewer Japanese die from the disease, because the cancer does not grow or progress. When Japanese men move to North America and eat more Westernized diets, cancers are faster-growing.

Although it has not been clinically proven (an argument you will hear time and time again from dairy boards and meat producers), you don’t have to be a rocket scientist to conclude that the Western high-fat, high-protein, low-fiber diet might have something to do with this discrepancy. The seven countries with the highest rates of breast cancer (over 20 deaths per 100,000 people per year) are countries where the average intake of fat is the highest (about 150 g a day). The seven countries with the lowest rates of breast cancer (about 5 per 100,000) occur in countries with the lowest intake of fats (less than 50 g a day). Prostate cancer rates are very similar.

However, another major protective factor may be soy in the Asian diet. A major 20-year study of 8000 Japanese men in Hawaii found a direct correlation between tofu consumption and lower rates of prostate cancer. Those who consumed tofu once a week or less were three times as likely to get prostate cancer as those who ate it daily. Other factors were measured, including fat intake, and tofu consumption was deemed to be most protective.

Cancer is believed to be a two-stage process– initiation, or exposure to a cancer-causing substance, and promotion, or stimulation by another substance that makes the first become active. There is considerable research going on today into substances that prevent the promotion stage and therefore halt or reverse cancer development. This is possible because there may be ten years or more between the time of tumor initiation and actual malignancy.

Soybeans contain several factors, which may inhibit cancer growth, which may explain why the Japanese men in those studies got prostate cancer, but succumbed to it far less often than did their Western counterparts.

Protease inhibitors are non-nutritive substances that are found in the reproductive parts of soybeans and other vegetables. Because they block the activity of an enzyme that aids the digestion of proteins, they were once thought to interfere with nutrition. The U.S. Dept. of Agriculture spent a lot of time and money trying to remove protease inhibitors from soybeans because they thought their removal would improve growth in children! However, it has been established that protease inhibitors are capable of neutralizing the effects of a large number of cancer-causing agents. Dr. Ann Kennedy, then of Harvard, now a leading researcher at the University of Pennsylvania School of Medicine, reported that even brief exposure of initiated and/or promoted cells to the Bowman-Birk Inhibitor (BBI), a protease inhibitor derived from soybeans, not only prevented transformation of the cells into cancers, but also “reprogrammed” their precancerous changes back to the “pre-initiation” stage.

In many laboratory studies, scientists have investigated protease inhibitors, especially BBI, and found that they inhibited cancers of the colon, lung, pancreas, mouth, esophagus, skin, and bladder. Evidently, protease inhibitors prevent the activation of specific genes that cause cancer, and they also protect against the damaging effects of free radicals and radiation.

Other substances in soybeans and other plant foods that seem to have anti-cancer properties are: polyphenols that have been reported to interfere with tumor promotion and to act as “garbage collectors”, disposing of cell-damaging mutagens and cancer-causing agents; phytates, the plant storage form of the mineral phosphorus, abundant in soybeans, and a chelator, a substance that binds with certain metals that may promote tumor growth and also acts as an antioxidant, preventing free radical damage; phytosterols, which are related to cholesterols, but found only in plant foods, and move straight through our intestines to our colons, protecting them against the harmful effects of bile acids and reducing the development of colon tumors; saponins, antioxidants which protect against free radical damage and, in laboratory investigations, have been shown to prevent mutations that can lead to cancer.

All of these substances, and several others which are still being investigated, occur in many plant foods, which is one very good reason why you should eat a plant-based diet with a wide variety of vegetables, fruits, grains and legumes. But soy contains them all, and more, which makes soy a valuable and potentially protective food.

Dr. Mark Messina and Virginia Messina, in their wonderfully informative book The Simple Soybean and Your Health, point out the intriguing results of over thirty different epidemiologic studies that have been conducted on many types of cancers and many varieties of soy foods. Most of these studies were comparisons between people living in different parts of Asia, who have generally similar diets and lifestyles (including fat intake), which makes them more useful than comparisons of Western and Asian diets, which have radically different average rates of fat consumption. They suggest that people who frequently consume soy foods have lower cancer rates than those who consume soy foods less often. In many of the studies, it seems that people who eat soy foods daily have about half the risk of cancer as those who eat soy foods only once or twice a week. For instance, a study in Singapore found that those women with the highest soy food consumption had less than half the breast cancer risk than those who consumed soy foods only rarely. A Japanese study showed that people who ate soy had only 1/7th the risk of rectal cancer of those who did not eat soy, and that eating soybeans and tofu lowered the colon cancer risk by 40%. In China, frequent consumers of soymilk had less than half the stomach cancer risk of those who did not drink it. Several Chinese studies (where smoking is more prevalent than in North America) found that lung cancer risk could be lowered by half with frequent tofu and other soy food consumption.

One thing that makes soy truly unique as a protective food is that it is one of the few foods that contains significant amounts of plant estrogens or phytoestrogens called isoflavones . These plant compounds are converted during the normal digestive process into a form of very weak estrogen. Back in 1982, Dr. Kenneth Setchell identified a phytoestrogen called equol in the urine of people who eat soy foods. Equol is structurally similar to the natural estrogen estradiol-17. Later, Dr. Herman Aldercreutz of the University of Helsinki found high levels of equol in the urine of Japanese men and women who ate a soy-rich traditional diet. He found low levels of equol in women who had breast cancer, as opposed to cancer-free women.

Scientists from several countries have found much higher levels of another isoflavone called genistein in the urine of people eating a traditional Japanese soy-rich diet than in those eating a typical Western diet. Genistein is a powerful anticarcinogen, found only in soybeans. It appears to inhibit enzymes that promote tumor growth. Test tube experiments show that genistein can block the growth of prostate cancer cells and breast cancer cells. As well, genistein helps to promote something called differentiation in cancerous cells. To explain this simply, the human body has specialized cells– bone cells, heart cells, skin cells, etc.– that have unique properties. When cells become cancerous, they “forget” what it was they were designed to do and begin to look the same. These so-called undifferentiated cells are very resistant to cancer therapies.

Another isoflavone found in soy is daidzein. Studies show that this isoflavone can also inhibit the growth of cancer cells and promote cell differentiation. Plant lignans are other phytoestrogens that occur widely in plant foods. Lignans are reported to have anticancer, antiviral, bactericidal, and fungistatic properties, and vegetarians have higher blood levels of them than do meat eaters.

Estrogens play a key role in the development of breast cancer. Among women who will eventually develop breast cancer, higher levels of active estrogen are present, apparently acting as a breast cancer promoter on a cellular level. For instance, estrogen increases cancer risk by binding to breast cells. Because isoflavones are so similar to human estrogen, they can attach to estrogen receptors, effectively blocking the human estrogen. But, because they are much, much weaker than estrogen, they don’t have the deadly effect that estrogens do. (Tamoxifen, a breast-cancer drug, works in the same way.)

Longer exposure to estrogen is a risk factor for breast cancer– women who start to menstruate early and have a late menopause are at higher risk, because they have been exposed to potent estrogens for a longer period. Remaining childless and not breastfeeding are further risk factors, again because during pregnancy and round-the-clock breastfeeding (before periods return) there are less active forms of circulating estrogen than during menstruation.

One of the reasons that fat (and meat) in the diet may be a major factor in hormone-related cancers such as breast and prostate is that a high-fat diet promotes high estrogen levels. At the University of California, Los Angeles, School of medicine, David Heber placed women on a very low-fat diet (less than 10% of calories) for only three weeks. In that short time the women dropped an average of 50% in serum estradiol (a form of estrogen) levels (one dropped 80%!) Another study in Boston measured blood hormone levels as well as urine excretion levels in vegetarian and meat-eating women. The vegetarian women had increased fecal excretion of estrogen, decreased levels of estrogen in the bile, and lower levels in the blood, 11 to 20 % lower than those measured in the meat-eating women. Many other studies, as well as the epidemiologic studies, point to a low-fat, low-meat diet as another way to lower the amount of estrogen exposure in a woman’s lifetime.

A longer time between menstrual periods also reduces exposure to estrogen. Kenneth Setchell, Ph.D., professor of Pediatrics at Children’s Hospital and Medical Center in Cincinnati, fed a group of women 60 g of textured soy protein daily for four weeks, and observed that the time between their menstrual cycles increased two to five days. 60 g of Miso lengthened this by another day.

(By the way, natural progesterone produced by the body or derived from wild yams and soy, protects against breast cancer. Synthetic progestins, however, have been linked to breast cancer.)

Obesity after menopause is also considered a risk factor, because large amounts of estrogen can be made in the subcutaneous fatty tissue. This is another reason to become fit and as slim as your body is comfortable being (see Chapters II and III).

Dr. Robert M. Kradjian, in his book Save Yourself from Breast Cancer, which I urge every woman and girl to read, paints a sad picture of the Western girl who, eating an estrogen-promoting high-fat, high-protein diet, will start menstruating at about age 12 and have only one or two children, who will not be breastfed for very long, if at all, thereby having a much longer exposure to potent estrogens than her sisters in “less developed” countries. About half of American girls exhibit breast or pubic hair development by age nine! In China, Japan, the Philippines, and Africa, where breast cancer rates are much lower, the average age of menarche is 16 or 17, as it was in the U.S. 100 years ago, and breastfeeding is prolonged, also as it was 75 or more years ago in North America.

IN MEN, estrogen also plays a part in prostate cancer. Estrogen is a precursor to androgens (male hormones), triggering the production of testosterone. Men with prostate cancer often have higher levels of testosterone than cancer-free men. The estrogen-blocking activities, as well as their tumor-inhibiting qualities, of soy isoflavones may therefore also play a part in preventing prostate cancer in men.

The cancer-protective claims for soy are called “speculative” by some, but the data is impressive. Soy foods have clear benefits in protecting against heart disease and have been proven to have no negative side effects; so many scientists are advising us not to wait years for definitive studies, but to start reaping the benefits of the mighty soybean NOW!

And, of course, soy is only one part of a healthy, protective diet. As I have mentioned before, it’s not a “magic bullet” or a “miracle food”. A varied complex-carbohydrate, high-fiber, low-fat, low-protein, plant-based diet with regular vigorous exercise is a most important component in a healthy life. As Dr. Robert M. Kradjian says, it’s unlikely that good health will come from a medicine bottle– we must seek protection from disease through improved nutrition. Adding soy to such a plan will only add more benefits, but this doesn’t mean isolating this or that protective substance from the soybean and taking it in a supplemental form. Just as we should get our antioxidants in the form of fresh fruits, vegetables, and legumes because we don’t even know what all them are yet, and we’re not sure how they all work in concert with one another, we aren’t sure if the protective components of soybeans will work “out of context”. Isoflavones may not do their work if not accompanied by the soy protein, for instance. It is a lesson that we in the West have yet to learn– to trust the power of whole foods, rather than specific nutrients.