The Cancer Prevention Potential of Soy
The latest study showing a remarkable 90% reduction in estrogen receptor-positive breast cancers in women who consumed lots of vegetables and soy (in lieu of a Western-style diet) provides persuasive evidence that compounds found in soy indeed have a breast cancerpreventive effect.25
For the past decade, a controversy has raged over whether people can reduce their risk of cancer by increasing their consumption of soy foods or soy supplements. In response to the debate, a number of studies were initiated in the 1990s to ascertain soy’s effects on human health.
Over the past few years, the results of these studies began to be released. While ignored by the mainstream media, the startling findings indicate that prostate and breast cancer risk could be cut in half if people only consumed more soy.25,49-51
Isoflavones derived from soy have shown great promise in providing natural protection against multipletypes of cancer.52-54 Isoflavones are phytochemical constituents of soy, with two of the best known being genistein and daidzein.
The isoflavones are believed to exert a number of positive biological effects on the human body, and many practitioners of integrative medicine (and even a small but growing number in mainstream medicine) now believe that consumption of soy and isoflavones can reduce the risk of many chronic diseases, including cancer, heart disease, and osteoporosis.49-59
Studies conducted in Asia found that Asian women, who consume many more isoflavones than American women, have significantly lower risks of developing breast cancer.60 Because animal studieshave shown that a diet high in soyand genistein can protect againstmammary, colon, and skin tumors,61it seemed reasonable to think thatsoy could also help prevent humancancers and, in particular, breastcancer. Yet many mainstream medical practitioners remain skepticalthat something as “simple” as soycould have such a profound effect onhuman health.
Soy, Estrogen, and Breast Cancer
Some in the medical establishment believe that soy isoflavones have no role in preventing serious diseases such as cancer. Others believe that soy isoflavones should not be used as nutritional supplements because isoflavones act as natural estrogens and could cause many of the same problems—such as increased risk of stroke—that synthetic estrogens are now known to cause.
In fact, soy isoflavones do not simply act as “natural” estrogens. Soy isoflavones are correctly classified as selective estrogen receptor modulators. Due to their unique molecular structure, soy isoflavones can act as either estrogen receptor agonists or receptor blockers. With this ability, soy isoflavones are thought by many to confer the beneficial effects of estrogen without its potentially dangerous side effects, especially in hormonally sensitive tissues found in both the breast and endometrium.62
Numerous studies show the potential benefits to women of incorporating soy in their diets to help prevent breast cancer. A landmark 1991 casecontrol study of women in Singapore, involving 200 case subjects and 420 control subjects, found that women with the highest consumption of soy-based products had a markedly decreased risk of developing breast cancer.63 An even larger Japanese case-control study in 1995, involving 1,186 subjects and 23,163 controls, also showed that women with increased tofu (soybean curd) intake had a significantly decreased risk of developing breast cancer compared with women who consumed small amounts of soy-based products such as tofu.51 Finally, a very large population-based, prospective study of 21,852 Japanese women aged 40-59 found that women with the highest intake of soy isoflavones reduced their risk of breast cancer by up to 54% compared with women with the lowest intake of soy isoflavones.60
Despite the evidence-based research showing soy isoflavones’ preventive effects on breast cancer, along with epidemiological studies highlighting the much lower rates of breast cancer among Asian women who consume significant amounts of soy-based products, some doctors still caution women against using soy-based foods and supplements.They contend that because soy isoflavones have been labeled as estrogen “mimics,” they could potentially worsen or even cause breast cancer. With the current knowledge that soy isoflavones act as selective estrogen receptor modulators and are not simply estrogen “mimics,” these arguments do not hold up.
In addition to being a chemopreventive supplement for breast cancer, soy isoflavones are also thought to be effective in warding off other types of cancer that afflict women, including endometrial cancer. A recent casecontrol study reported the effects of soy isoflavones and other phytoestrogens on the risk of developing endometrial cancer.64 The study compared 500 women aged 35-79 who developed endometrial cancer between 1996 and 1999 with 470 age- and ethnicity-matched controls. As in studies examining the effects of isoflavones on breast cancer, this study showed that women with a higher intake of soy isoflavones had a significantly lower risk of developing endometrial cancer. Even more interesting was that the levels of isoflavones needed to provide protection against endometrial cancer were found to be much lower than the amount believed necessary to protect against breast cancer.
Soy Counteracts Prostate Cancer in Men
Both animal and human studies have shown that soy isoflavones can help protect men from prostate cancer by slowing and even preventing the disease.65,66 Prostate cancer is the most common cancer in men and the second leading cause of death from cancer (after lung cancer) among men.67 As is the case concerning breast cancer in women, large epidemiological studies have shown that Asian men who consume large amounts of soy-based foods have a significantly lower incidence of prostate cancer, compared with their Western counterparts.68
Researchers found that soybean products, as well as other East Asian dietary staples such as fish and tofu, were associated with a decreased risk of prostate cancer in Japanese men.68 Specifically, men who consumed the greatest amounts of soybeans and tofu were 47% and 53% less likely, respectively, to develop prostate cancer than those who consumed the smallest amounts. Furthermore, in men who consumed the greatest product natto, the prostate cancer incidence was reduced by a remarkable 75%.
Finally, in a case-control study published in January 2004, Japanese researchers sought to ascertain whether a high serum concentration of phytoestrogens reduces the risk of prostate cancer. The researchers collected lifestyle information and serum samples from more than 14,000 Japanese men in 1988-90, who were tracked until 1999. Phytoestrogens and sex hormones stored in serum were measured in 2002, and 52 case subjects and 151 controls were identified. This study clearly established that elevated serum levels of all three phytoestrogens assessed—genistein, daidzein, and equol—imparted a strong protective effect against prostate cancer.69 Men with the highest circulating levels of genistein, daidzein, and equol reduced their risk of prostate cancer by 62%, 59%, and 66%, respectively.
Soy can be added to one’s diet in many ways, and it is increasingly being used in breast health dietary supplement formulas.
Why Fruits are Important
The body is bombarded with carcinogens on a daily basis. These cancer-causing agents include pesticides, over-cooked food, alcohol, food additives, tobacco, fungal mutagens, and industrial pollutants. While avoiding carcinogens is difficult, it may be possible to mitigate their lethal effects by providing the body with a specific plant extract that facilitates the detoxification and removal of these dangerous substances from the body.
A compound called D-glucarate is found in grapefruit, apples, oranges, broccoli, and Brussels sprouts.70,71 D-Glucarate has been shown to protect against cancer-causing agents by supporting detoxification and removal of dangerous chemicals, and also by protecting against the mutating effects that these carcinogens induce on cellular DNA.72
There are several mechanisms by which the body detoxifies itself. One way of guarding against toxic overload involves a pathway of detoxification in the body whereby carcinogens are combined with water-soluble substances, thus making them more easily removed from the body. This process is called glucuronidation, and D-glucarate has been shown to support this important detoxification mechanism.72
How Does D-Glucarate Work?
D-Glucarate functions by inhibiting the dangerous beta-glucuronidase enzyme, thus protecting the critical “glucuronidation” detoxification mechanism. One example of the importance of glucuronidation can be seen in the risk factors for breast cancer. Excess levels of 16 alphahydroxyestrone and the beta-glucuronidase enzyme are associated with an increased incidence of breast cancer.73 D-Glucarate is thought to decrease estrogen levels by affecting estrogen’s elimination.
Normally, estrogen is conjugated with glucurate in the liver (glucuronidation), and then excreted in the bile. A bacterial enzyme in the intestine called beta-glucuronidase can break the estrogen-glucuronide bond, allowing estrogen to be reabsorbed. D-Glucarate works at this step by inhibiting beta-glucuronidase.73 Blocking this enzyme is thought to decrease the amount of estrogen that is reabsorbed and thus to lower circulating estrogen levels.
Research studies have shown that D-glucarate inhibits mammary tumor incidence.74,75 One study in rats that already had breast cancer showed that oral D-glucarate administration resulted in a 50% inhibition of beta-glucuronidase, which led to a 30% reduction in mammary tumor growth during the promotion stage and a four-fold reduction in the absolute number of tumors.76 Another study showed a more than 70% decrease in mammary tumor development in rats exposed to carcinogens who were also administered D-glucarate.77 Still another study looked at the effects of D-glucarate on the initiation and promotional stages of mammary cancer. The results showed a reduction of 28% during the initiation stage, while cell replication was reduced by 42% during the promotion stage.78 Inhibition at the initiation stage is a very important part of D-glucarate’s actions, as it lessens the risk that cancer will even start.
Eating lots of the right fruits and vegetables supplies the body with D-glucarate. It is also available in dietary supplements designed to support breast health.